MapReducer (OSHDB API 0.5.9 API)

java.lang.Object
- org.heigit.bigspatialdata.oshdb.api.mapreducer.MapReducer<X>

Type Parameters:

X - the type that is returned by the currently set of mapper function. the next added mapper function will be called with a parameter of this type as input

All Implemented Interfaces:

Serializable, Mappable<X>

Direct Known Subclasses:

MapReducerIgniteAffinityCall, MapReducerIgniteLocalPeek, MapReducerIgniteScanQuery, MapReducerJdbcMultithread, MapReducerJdbcSinglethread
```
public abstract class MapReducer<X>
extends Object
implements Mappable<X>, Serializable
```
Main class of oshdb's "functional programming" API.
It accepts a list of filters, transformation `map` functions a produces a result when calling the `reduce` method (or one of its shorthand versions like `sum`, `count`, etc.).

You can set a list of filters that are applied on the raw OSM data, for example you can filter:
- geometrically by an area of interest (bbox or polygon)
- by osm tags (key only or key/value)
- by OSM type
- custom filter callback
Depending on the used data "view", the MapReducer produces either "snapshots" or evaluated all modifications ("contributions") of the matching raw OSM data.

These data can then be transformed arbitrarily by user defined `map` functions (which take one of these entity snapshots or modifications as input an produce an arbitrary output) or `flatMap` functions (which can return an arbitrary number of results per entity snapshot/contribution). It is possible to chain together any number of transformation functions.

Finally, one can either use one of the pre-defined result-generating functions (e.g. `sum`, `count`, `average`, `uniq`), or specify a custom `reduce` procedure.

If one wants to get results that are aggregated by timestamp (or some other index), one can use the `aggregateByTimestamp` or `aggregateBy` functionality that automatically handles the grouping of the output data.

For more complex analyses, it is also possible to enable the grouping of the input data by the respective OSM ID. This can be used to view at the whole history of entities at once.
See Also:

Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`protected OSHDBBoundingBox`	`bboxFilter`
`protected OSHDBJdbc`	`keytables`
`protected OSHDBDatabase`	`oshdb`
`protected Long`	`timeout`
`protected OSHDBTimestampList`	`tstamps`
`protected EnumSet<OSMType>`	`typeFilter`

Constructor Summary

Constructors
Modifier	Constructor and Description
`protected`	`MapReducer(MapReducer<?> obj)`
`protected`	`MapReducer(OSHDBDatabase oshdb, Class<? extends OSHDBMapReducible> forClass)`

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods Default Methods Deprecated Methods
Modifier and Type	Method and Description
`<U extends Comparable<U> & Serializable> MapAggregator<U,X>`	`aggregateBy(SerializableFunction<X,U> indexer)` Sets a custom aggregation function that is used to group output results into.
`<U extends Comparable<U> & Serializable> MapAggregator<U,X>`	`aggregateBy(SerializableFunction<X,U> indexer, Collection<U> zerofill)` Sets a custom aggregation function that is used to group output results into.
`<U extends Comparable<U> & Serializable,P extends org.locationtech.jts.geom.Geometry & org.locationtech.jts.geom.Polygonal> MapAggregator<U,X>`	`aggregateByGeometry(Map<U,P> geometries)` Sets up automatic aggregation by geometries.
`MapAggregator<OSHDBTimestamp,X>`	`aggregateByTimestamp()` Sets up automatic aggregation by timestamp.
`MapAggregator<OSHDBTimestamp,X>`	`aggregateByTimestamp(SerializableFunction<X,OSHDBTimestamp> indexer)` Sets up aggregation by a custom time index.
`MapReducer<X>`	`areaOfInterest(OSHDBBoundingBox bboxFilter)` Set the area of interest to the given bounding box.
`<P extends org.locationtech.jts.geom.Geometry & org.locationtech.jts.geom.Polygonal> MapReducer<X>`	`areaOfInterest(P polygonFilter)` Set the area of interest to the given polygon.
`Double`	`average()` Calculates the averages of the results.
`<R extends Number> Double`	`average(SerializableFunction<X,R> mapper)` Calculates the average of the results provided by a given `mapper` function.
`List<X>`	`collect()` Collects all results into a List.
`protected abstract MapReducer<X>`	`copy()`
`Integer`	`count()` Counts the number of results.
`Integer`	`countUniq()` Counts all unique values of the results.
`Double`	`estimatedMedian()` Returns an estimate of the median of the results.
`<R extends Number> Double`	`estimatedMedian(SerializableFunction<X,R> mapper)` Returns an estimate of the median of the results after applying the given map function.
`Double`	`estimatedQuantile(double q)` Returns an estimate of a requested quantile of the results.
`<R extends Number> Double`	`estimatedQuantile(SerializableFunction<X,R> mapper, double q)` Returns an estimate of a requested quantile of the results after applying the given map function.
`DoubleUnaryOperator`	`estimatedQuantiles()` Returns a function that computes estimates of arbitrary quantiles of the results.
`List<Double>`	`estimatedQuantiles(Iterable<Double> q)` Returns an estimate of the quantiles of the results.
`<R extends Number> DoubleUnaryOperator`	`estimatedQuantiles(SerializableFunction<X,R> mapper)` Returns a function that computes estimates of arbitrary quantiles of the results after applying the given map function.
`<R extends Number> List<Double>`	`estimatedQuantiles(SerializableFunction<X,R> mapper, Iterable<Double> q)` Returns an estimate of the quantiles of the results after applying the given map function.
`MapReducer<X>`	`filter(SerializablePredicate<X> f)` Adds a custom arbitrary filter that gets executed in the current transformation chain.
`<R> MapReducer<R>`	`flatMap(SerializableFunction<X,Iterable<R>> flatMapper)` Set an arbitrary `flatMap` transformation function, which returns list with an arbitrary number of results per input data entry.
`protected <R,S> S`	`flatMapReduceCellsOSMContributionGroupedById(SerializableFunction<List<OSMContribution>,Iterable<R>> mapper, SerializableSupplier<S> identitySupplier, SerializableBiFunction<S,R,S> accumulator, SerializableBinaryOperator<S> combiner)` Generic "flat" version of the map-reduce used by the `OSMContributionView`, with by-osm-id grouped input to the `mapper` function.
`protected <R,S> S`	`flatMapReduceCellsOSMEntitySnapshotGroupedById(SerializableFunction<List<OSMEntitySnapshot>,Iterable<R>> mapper, SerializableSupplier<S> identitySupplier, SerializableBiFunction<S,R,S> accumulator, SerializableBinaryOperator<S> combiner)` Generic "flat" version of the map-reduce used by the `OSMEntitySnapshotView`, with by-osm-id grouped input to the `mapper` function.
`protected Stream<X>`	`flatMapStreamCellsOSMContributionGroupedById(SerializableFunction<List<OSMContribution>,Iterable<X>> mapper)`
`protected Stream<X>`	`flatMapStreamCellsOSMEntitySnapshotGroupedById(SerializableFunction<List<OSMEntitySnapshot>,Iterable<X>> mapper)`
`void`	`forEach(SerializableConsumer<X> action)` Deprecated. only for testing purposes, use `.stream().forEach()` instead
`protected Iterable<XYGridTree.CellIdRange>`	`getCellIdRanges()`
`protected CellIterator.OSMEntityFilter`	`getFilter()`
`protected <P extends org.locationtech.jts.geom.Geometry & org.locationtech.jts.geom.Polygonal> P`	`getPolyFilter()`
`protected CellIterator.OSHEntityFilter`	`getPreFilter()`
`protected TagInterpreter`	`getTagInterpreter()`
`protected TagTranslator`	`getTagTranslator()`
`MapReducer<List<X>>`	`groupByEntity()` Groups the input data (osm entity snapshot or contributions) by their respective entity's ids before feeding them into further transformation functions.
`boolean`	`isCancelable()` Returns if the current backend can be canceled (e.g.
`MapReducer<X>`	`keytables(OSHDBJdbc keytables)` Sets the keytables database to use in the calculations to resolve strings (osm tags, roles) into internally used identifiers.
`<R> MapReducer<R>`	`map(SerializableFunction<X,R> mapper)` Set an arbitrary `map` transformation function.
`protected <R,S> S`	`mapReduceCellsOSMContribution(SerializableFunction<OSMContribution,R> mapper, SerializableSupplier<S> identitySupplier, SerializableBiFunction<S,R,S> accumulator, SerializableBinaryOperator<S> combiner)` Generic map-reduce used by the `OSMContributionView`.
`protected <R,S> S`	`mapReduceCellsOSMEntitySnapshot(SerializableFunction<OSMEntitySnapshot,R> mapper, SerializableSupplier<S> identitySupplier, SerializableBiFunction<S,R,S> accumulator, SerializableBinaryOperator<S> combiner)` Generic map-reduce used by the `OSMEntitySnapshotView`.
`protected Stream<X>`	`mapStreamCellsOSMContribution(SerializableFunction<OSMContribution,X> mapper)`
`protected Stream<X>`	`mapStreamCellsOSMEntitySnapshot(SerializableFunction<OSMEntitySnapshot,X> mapper)`
`MapReducer<X>`	`osmEntityFilter(SerializablePredicate<OSMEntity> f)` Adds a custom arbitrary filter that gets executed for each osm entity and determines if it should be considered for this analyis or not.
`MapReducer<X>`	`osmTag(Collection<? extends OSMTagInterface> tags)` Adds an osm tag filter: The analysis will be restricted to osm entities that have at least one of the supplied tags (key=value pairs or key=*).
`MapReducer<X>`	`osmTag(OSMTagInterface tag)` Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key (with an arbitrary value), or this tag key and value.
`MapReducer<X>`	`osmTag(String key)` Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key (with an arbitrary value).
`MapReducer<X>`	`osmTag(String key, Collection<String> values)` Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key and one of the given values.
`MapReducer<X>`	`osmTag(String key, Pattern valuePattern)` Adds an osm tag filter: The analysis will be restricted to osm entities that have a tag with the given key and whose value matches the given regular expression pattern.
`MapReducer<X>`	`osmTag(String key, String value)` Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key and value.
`default M`	`osmType(OSMType type1, OSMType... otherTypes)` Limits the analysis to the given osm entity types.
`MapReducer<X>`	`osmType(Set<OSMType> typeFilter)` Limits the analysis to the given osm entity types.
`default M`	`osmTypes(EnumSet<OSMType> typeFilter)` Deprecated. replaced by `osmType(OSMType, OSMType...)`
`default M`	`osmTypes(OSMType type1, OSMType... otherTypes)` Deprecated. replaced by `osmType(OSMType, OSMType...)`
`<S> S`	`reduce(SerializableSupplier<S> identitySupplier, SerializableBiFunction<S,X,S> accumulator, SerializableBinaryOperator<S> combiner)` Generic map-reduce routine.
`X`	`reduce(SerializableSupplier<X> identitySupplier, SerializableBinaryOperator<X> accumulator)` Generic map-reduce routine (shorthand syntax).
`Stream<X>`	`stream()` Returns all results as a Stream.
`Number`	`sum()` Sums up the results.
`<R extends Number> R`	`sum(SerializableFunction<X,R> mapper)` Sums up the results provided by a given `mapper` function.
`MapReducer<X>`	`tagInterpreter(TagInterpreter tagInterpreter)` Sets the tagInterpreter to use in the analysis.
`MapReducer<X>`	`timestamps(OSHDBTimestampList tstamps)` Set the timestamps for which to perform the analysis.
`MapReducer<X>`	`timestamps(String isoDate)` Sets a single timestamp for which to perform the analysis at.
`MapReducer<X>`	`timestamps(String isoDateStart, String isoDateEnd)` Sets two timestamps (start and end date) for which to perform the analysis.
`MapReducer<X>`	`timestamps(String isoDateStart, String isoDateEnd, OSHDBTimestamps.Interval interval)` Set the timestamps for which to perform the analysis in a regular interval between a start and end date.
`MapReducer<X>`	`timestamps(String isoDateFirst, String isoDateSecond, String... isoDateMore)` Sets multiple arbitrary timestamps for which to perform the analysis.
`Set<X>`	`uniq()` Gets all unique values of the results.
`<R> Set<R>`	`uniq(SerializableFunction<X,R> mapper)` Gets all unique values of the results provided by a given mapper function.
`Double`	`weightedAverage(SerializableFunction<X,WeightedValue> mapper)` Calculates the weighted average of the results provided by the `mapper` function.
`default M`	`where(Collection<OSMTag> keyValuePairs)` Deprecated. replaced by `osmTag(Collection)`
`default M`	`where(OSMTag tag)` Deprecated. replaced by `osmTag(OSMTagInterface)`
`default M`	`where(OSMTagKey key)` Deprecated. replaced by `osmTag(OSMTagInterface)`
`default M`	`where(SerializablePredicate<OSMEntity> f)` Deprecated. replaced by `osmEntityFilter(org.heigit.bigspatialdata.oshdb.api.generic.function.SerializablePredicate<org.heigit.bigspatialdata.oshdb.osm.OSMEntity>)`
`default M`	`where(String key)` Deprecated. replaced by `osmTag(String)`
`default M`	`where(String key, Collection<String> values)` Deprecated. replaced by `osmTag(String, Collection)`
`default M`	`where(String key, Pattern valuePattern)` Deprecated. replaced by `osmTag(String, Pattern)`
`default M`	`where(String key, String value)` Deprecated. replaced by `osmTag(String, String)`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
 - oshdb
```
protected OSHDBDatabase oshdb
```
 - keytables
```
protected transient OSHDBJdbc keytables
```
 - timeout
```
protected Long timeout
```
 - tstamps
```
protected OSHDBTimestampList tstamps
```
 - bboxFilter
```
protected OSHDBBoundingBox bboxFilter
```
 - typeFilter
```
protected EnumSet<OSMType> typeFilter
```
- Constructor Detail
 - MapReducer
```
protected MapReducer(OSHDBDatabase oshdb,
 Class<? extends OSHDBMapReducible> forClass)
```
 - MapReducer
```
protected MapReducer(MapReducer<?> obj)
```
- Method Detail
 - isCancelable
```
public boolean isCancelable()
```
 Returns if the current backend can be canceled (e.g. in a query timeout).
 - copy
```
@NotNull
protected abstract MapReducer<X> copy()
```
 - keytables
```
@Contract(pure=true)
public MapReducer<X> keytables(OSHDBJdbc keytables)
```
 Sets the keytables database to use in the calculations to resolve strings (osm tags, roles) into internally used identifiers. If this function is never called, the main database (specified during the construction of this object) is used for this.
 
 Parameters:
 
 keytables - the database to use for resolving strings into internal identifiers
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - tagInterpreter
```
@Contract(pure=true)
public MapReducer<X> tagInterpreter(TagInterpreter tagInterpreter)
```
 Sets the tagInterpreter to use in the analysis. The tagInterpreter is used internally to determine the geometry type of osm entities (e.g. an osm way can become either a LineString or a Polygon, depending on its tags). Normally, this is generated automatically for the user. But for example, if one doesn't want to use the DefaultTagInterpreter, it is possible to use this function to supply their own tagInterpreter.
 
 Parameters:
 
 tagInterpreter - the tagInterpreter object to use in the processing of osm entities
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - areaOfInterest
```
@Contract(pure=true)
public MapReducer<X> areaOfInterest(@NotNull
 OSHDBBoundingBox bboxFilter)
```
 Set the area of interest to the given bounding box. Only objects inside or clipped by this bbox will be passed on to the analysis' `mapper` function.
 
 Parameters:
 
 bboxFilter - the bounding box to query the data in
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - areaOfInterest
```
@Contract(pure=true)
public  MapReducer<X> areaOfInterest(@NotNull
 P polygonFilter)
```
 Set the area of interest to the given polygon. Only objects inside or clipped by this polygon will be passed on to the analysis' `mapper` function.
 
 Parameters:
 
 polygonFilter - the bounding box to query the data in
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - timestamps
```
@Contract(pure=true)
public MapReducer<X> timestamps(OSHDBTimestampList tstamps)
```
 Set the timestamps for which to perform the analysis.
 Depending on the *View*, this has slightly different semantics:
 - For the OSMEntitySnapshotView it will set the time slices at which to take the "snapshots"
 - For the OSMContributionView it will set the time interval in which to look for osm contributions (only the first and last timestamp of this list are contributing).
 Additionally, these timestamps are used in the `aggregateByTimestamp` functionality.
 Parameters:
 
 tstamps - an object (implementing the OSHDBTimestampList interface) which provides the timestamps to do the analysis for
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - timestamps
```
@Contract(pure=true)
public MapReducer<X> timestamps(String isoDateStart,
 String isoDateEnd,
 OSHDBTimestamps.Interval interval)
```
 Set the timestamps for which to perform the analysis in a regular interval between a start and end date.
 See timestamps(OSHDBTimestampList) for further information.
 
 Parameters:
 
 isoDateStart - an ISO 8601 date string representing the start date of the analysis
 
 isoDateEnd - an ISO 8601 date string representing the end date of the analysis
 
 interval - the interval between the timestamps to be used in the analysis
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - timestamps
```
@Contract(pure=true)
public MapReducer<X> timestamps(String isoDate)
```
 Sets a single timestamp for which to perform the analysis at.
 Useful in combination with the OSMEntitySnapshotView when not performing further aggregation by timestamp.
 
 See timestamps(OSHDBTimestampList) for further information.
 
 Parameters:
 
 isoDate - an ISO 8601 date string representing the date of the analysis
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - timestamps
```
@Contract(pure=true)
public MapReducer<X> timestamps(String isoDateStart,
 String isoDateEnd)
```
 Sets two timestamps (start and end date) for which to perform the analysis.
 Useful in combination with the OSMContributionView when not performing further aggregation by timestamp.
 
 See timestamps(OSHDBTimestampList) for further information.
 
 Parameters:
 
 isoDateStart - an ISO 8601 date string representing the start date of the analysis
 
 isoDateEnd - an ISO 8601 date string representing the end date of the analysis
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - timestamps
```
@Contract(pure=true)
public MapReducer<X> timestamps(String isoDateFirst,
 String isoDateSecond,
 String... isoDateMore)
```
 Sets multiple arbitrary timestamps for which to perform the analysis.
 Note for programmers wanting to use this method to supply an arbitrary number (n>=1) of timestamps: You may supply the same time string multiple times, which will be de-duplicated internally. E.g. you can call the method like this: .timestamps(dateArr[0], dateArr[0], dateArr)
 
 See timestamps(OSHDBTimestampList) for further information.
 
 Parameters:
 
 isoDateFirst - an ISO 8601 date string representing the start date of the analysis
 
 isoDateSecond - an ISO 8601 date string representing the second date of the analysis
 
 isoDateMore - more ISO 8601 date strings representing the remaining timestamps of the analysis
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmType
```
@Contract(pure=true)
public MapReducer<X> osmType(Set<OSMType> typeFilter)
```
 Limits the analysis to the given osm entity types.
 
 Parameters:
 
 typeFilter - the set of osm types to filter (e.g. `EnumSet.of(OSMType.WAY)`)
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmEntityFilter
```
@Contract(pure=true)
public MapReducer<X> osmEntityFilter(SerializablePredicate<OSMEntity> f)
```
 Adds a custom arbitrary filter that gets executed for each osm entity and determines if it should be considered for this analyis or not.
 
 Parameters:
 
 f - the filter function to call for each osm entity
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmTag
```
@Contract(pure=true)
public MapReducer<X> osmTag(String key)
```
 Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key (with an arbitrary value).
 
 Parameters:
 
 key - the tag key to filter the osm entities for
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmTag
```
@Contract(pure=true)
public MapReducer<X> osmTag(OSMTagInterface tag)
```
 Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key (with an arbitrary value), or this tag key and value.
 
 Parameters:
 
 tag - the tag (key, or key and value) to filter the osm entities for
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmTag
```
@Contract(pure=true)
public MapReducer<X> osmTag(String key,
 String value)
```
 Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key and value.
 
 Parameters:
 
 key - the tag to filter the osm entities for
 
 value - the tag value to filter the osm entities for
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmTag
```
@Contract(pure=true)
public MapReducer<X> osmTag(String key,
 Collection<String> values)
```
 Adds an osm tag filter: The analysis will be restricted to osm entities that have this tag key and one of the given values.
 
 Parameters:
 
 key - the tag key to filter the osm entities for
 
 values - an array of tag values to filter the osm entities for
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmTag
```
@Contract(pure=true)
public MapReducer<X> osmTag(String key,
 Pattern valuePattern)
```
 Adds an osm tag filter: The analysis will be restricted to osm entities that have a tag with the given key and whose value matches the given regular expression pattern.
 
 Parameters:
 
 key - the tag key to filter the osm entities for
 
 valuePattern - a regular expression which the tag value of the osm entity must match
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - osmTag
```
@Contract(pure=true)
public MapReducer<X> osmTag(Collection<? extends OSMTagInterface> tags)
```
 Adds an osm tag filter: The analysis will be restricted to osm entities that have at least one of the supplied tags (key=value pairs or key=*).
 
 Parameters:
 
 tags - the tags (key/value pairs or key=*) to filter the osm entities for
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - map
```
@Contract(pure=true)
public <R> MapReducer<R> map(SerializableFunction<X,R> mapper)
```
 Set an arbitrary `map` transformation function.
 
 Specified by:
 
 map in interface Mappable<X>
 
 Type Parameters:
 
 R - an arbitrary data type which is the return type of the transformation `map` function
 
 Parameters:
 
 mapper - function that will be applied to each data entry (osm entity snapshot or contribution)
 
 Returns:
 
 a modified copy of this MapReducer object operating on the transformed type (<R>)
 - flatMap
```
@Contract(pure=true)
public <R> MapReducer<R> flatMap(SerializableFunction<X,Iterable<R>> flatMapper)
```
 Set an arbitrary `flatMap` transformation function, which returns list with an arbitrary number of results per input data entry. The results of this function will be "flattened", meaning that they can be for example transformed again by setting additional `map` functions.
 
 Specified by:
 
 flatMap in interface Mappable<X>
 
 Type Parameters:
 
 R - an arbitrary data type which is the return type of the transformation `map` function
 
 Parameters:
 
 flatMapper - function that will be applied to each data entry (osm entity snapshot or contribution) and returns a list of results
 
 Returns:
 
 a modified copy of this MapReducer object operating on the transformed type (<R>)
 - filter
```
@Contract(pure=true)
public MapReducer<X> filter(SerializablePredicate<X> f)
```
 Adds a custom arbitrary filter that gets executed in the current transformation chain.
 
 Specified by:
 
 filter in interface Mappable<X>
 
 Parameters:
 
 f - the filter function that determines if the respective data should be passed on (when f returns true) or discarded (when f returns false)
 
 Returns:
 
 a modified copy of this mapReducer (can be used to chain multiple commands together)
 - groupByEntity
```
@Contract(pure=true)
public MapReducer<List<X>> groupByEntity()
 throws UnsupportedOperationException
```
 Groups the input data (osm entity snapshot or contributions) by their respective entity's ids before feeding them into further transformation functions. This can be used to do more complex analysis on the osm data, that requires one to know about the full editing history of individual osm entities.
 This needs to be called before any `map` or `flatMap` transformation functions have been set. Otherwise a runtime exception will be thrown.
 
 Returns:
 
 the MapReducer object which applies its transformations on (by entity id grouped) lists of the input data
 
 Throws:
 
 UnsupportedOperationException - if this is called after some map (or flatMap) functions have already been set
 
 UnsupportedOperationException - if this is called when a grouping has already been activated
 - aggregateBy
```
@Contract(pure=true)
public  & Serializable> MapAggregator<U,X> aggregateBy(SerializableFunction<X,U> indexer,
 Collection zerofill)
```
 Sets a custom aggregation function that is used to group output results into.
 
 Type Parameters:
 
 U - the data type of the values used to aggregate the output. has to be a comparable type
 
 Parameters:
 
 indexer - a function that will be called for each input element and returns a value that will be used to group the results by
 
 zerofill - a collection of values that are expected to be present in the result
 
 Returns:
 
 a MapAggregator object with the equivalent state (settings, filters, map function, etc.) of the current MapReducer object
 - aggregateBy
```
@Contract(pure=true)
public  & Serializable> MapAggregator<U,X> aggregateBy(SerializableFunction<X,U> indexer)
```
 Sets a custom aggregation function that is used to group output results into.
 
 Type Parameters:
 
 U - the data type of the values used to aggregate the output. has to be a comparable type
 
 Parameters:
 
 indexer - a function that will be called for each input element and returns a value that will be used to group the results by
 
 Returns:
 
 a MapAggregator object with the equivalent state (settings, filters, map function, etc.) of the current MapReducer object
 - aggregateByTimestamp
```
@Contract(pure=true)
public MapAggregator<OSHDBTimestamp,X> aggregateByTimestamp()
 throws UnsupportedOperationException
```
 Sets up automatic aggregation by timestamp.
 In the OSMEntitySnapshotView, the snapshots' timestamp will be used directly to aggregate results into. In the OSMContributionView, the timestamps of the respective data modifications will be matched to corresponding time intervals (that are defined by the `timestamps` setting here).
 
 Cannot be used together with the `groupByEntity()` setting enabled.
 
 Returns:
 
 a MapAggregator object with the equivalent state (settings, filters, map function, etc.) of the current MapReducer object
 
 Throws:
 
 UnsupportedOperationException - if this is called when the `groupByEntity()` mode has been activated
 - aggregateByTimestamp
```
public MapAggregator<OSHDBTimestamp,X> aggregateByTimestamp(SerializableFunction<X,OSHDBTimestamp> indexer)
 throws UnsupportedOperationException
```
 Sets up aggregation by a custom time index.
 The timestamps returned by the supplied indexing function are matched to the corresponding time intervals.
 
 Parameters:
 
 indexer - a callback function that return a timestamp object for each given data. Note that if this function returns timestamps outside of the supplied timestamps() interval results may be undefined
 
 Returns:
 
 a MapAggregator object with the equivalent state (settings, filters, map function, etc.) of the current MapReducer object
 
 Throws:
 
 UnsupportedOperationException
 - aggregateByGeometry
```
@Contract(pure=true)
public  & Serializable,P extends org.locationtech.jts.geom.Geometry & org.locationtech.jts.geom.Polygonal> MapAggregator<U,X> aggregateByGeometry(Map<U,P> geometries)
 throws UnsupportedOperationException
```
 Sets up automatic aggregation by geometries.
 Cannot be used together with the `groupByEntity()` setting enabled.
 
 Returns:
 
 a MapAggregator object with the equivalent state (settings, filters, map function, etc.) of the current MapReducer object
 
 Throws:
 
 UnsupportedOperationException - if this is called when the `groupByEntity()` mode has been activated
 
 UnsupportedOperationException - when called after any map or flatMap functions are set
 - reduce
```
@Contract(pure=true)
public <S> S reduce(SerializableSupplier<S> identitySupplier,
 SerializableBiFunction<S,X,S> accumulator,
 SerializableBinaryOperator<S> combiner)
 throws Exception
```
 Generic map-reduce routine.
 The combination of the used types and identity/reducer functions must make "mathematical" sense:
 - the accumulator and combiner functions need to be associative,
 - values generated by the identitySupplier factory must be an identity for the combiner function: `combiner(identitySupplier(),x)` must be equal to `x`,
 - the combiner function must be compatible with the accumulator function: `combiner(u, accumulator(identitySupplier(), t)) == accumulator.apply(u, t)`
 Functionally, this interface is similar to Java8 Stream's reduce(identity,accumulator,combiner) interface.
 Type Parameters:
 
 S - the data type used to contain the "reduced" (intermediate and final) results
 
 Parameters:
 
 identitySupplier - a factory function that returns a new starting value to reduce results into (e.g. when summing values, one needs to start at zero)
 
 accumulator - a function that takes a result from the `mapper` function (type <R>) and an accumulation value (type <S>, e.g. the result of `identitySupplier()`) and returns the "sum" of the two; contrary to `combiner`, this function is allowed to alter (mutate) the state of the accumulation value (e.g. directly adding new values to an existing Set object)
 
 combiner - a function that calculates the "sum" of two <S> values; this function must be pure (have no side effects), and is not allowed to alter the state of the two input objects it gets!
 
 Returns:
 
 the result of the map-reduce operation, the final result of the last call to the `combiner` function, after all `mapper` results have been aggregated (in the `accumulator` and `combiner` steps)
 
 Throws:
 
 UnsupportedOperationException - if the used oshdb database backend doesn't implement the required reduce operation.
 
 Exception - if during the reducing operation an exception happens (see the respective implementations for details).
 - reduce
```
@Contract(pure=true)
public X reduce(SerializableSupplier<X> identitySupplier,
 SerializableBinaryOperator<X> accumulator)
 throws Exception
```
 Generic map-reduce routine (shorthand syntax).
 This variant is shorter to program than `reduce(identitySupplier, accumulator, combiner)`, but can only be used if the result type is the same as the current `map`ped type <X>. Also this variant can be less efficient since it cannot benefit from the mutability freedoms the accumulator+combiner approach has.
 
 The combination of the used types and identity/reducer functions must make "mathematical" sense:
 - the accumulator function needs to be associative,
 - values generated by the identitySupplier factory must be an identity for the accumulator function: `accumulator(identitySupplier(),x)` must be equal to `x`,
 Functionally, this interface is similar to Java8 Stream's reduce(identity,accumulator) interface.
 Parameters:
 
 identitySupplier - a factory function that returns a new starting value to reduce results into (e.g. when summing values, one needs to start at zero)
 
 accumulator - a function that takes a result from the `mapper` function (type <X>) and an accumulation value (also of type <X>, e.g. the result of `identitySupplier()`) and returns the "sum" of the two; contrary to `combiner`, this function is not to alter (mutate) the state of the accumulation value (e.g. directly adding new values to an existing Set object)
 
 Returns:
 
 the result of the map-reduce operation, the final result of the last call to the `combiner` function, after all `mapper` results have been aggregated (in the `accumulator` and `combiner` steps)
 
 Throws:
 
 Exception
 - sum
```
@Contract(pure=true)
public Number sum()
 throws Exception
```
 Sums up the results.
 The current data values need to be numeric (castable to "Number" type), otherwise a runtime exception will be thrown.
 
 Returns:
 
 the sum of the current data
 
 Throws:
 
 UnsupportedOperationException - if the data cannot be cast to numbers
 
 Exception
 - sum
```
@Contract(pure=true)
public <R extends Number> R sum(SerializableFunction<X,R> mapper)
 throws Exception
```
 Sums up the results provided by a given `mapper` function.
 This is a shorthand for `.map(mapper).sum()`, with the difference that here the numerical return type of the `mapper` is ensured.
 
 Type Parameters:
 
 R - the numeric type that is returned by the `mapper` function
 
 Parameters:
 
 mapper - function that returns the numbers to sum up
 
 Returns:
 
 the summed up results of the `mapper` function
 
 Throws:
 
 Exception
 - count
```
@Contract(pure=true)
public Integer count()
 throws Exception
```
 Counts the number of results.
 
 Returns:
 
 the total count of features or modifications, summed up over all timestamps
 
 Throws:
 
 Exception
 - uniq
```
@Contract(pure=true)
public Set<X> uniq()
 throws Exception
```
 Gets all unique values of the results.
 For example, this can be used together with the OSMContributionView to get the total amount of unique users editing specific feature types.
 
 Returns:
 
 the set of distinct values
 
 Throws:
 
 Exception
 - uniq
```
@Contract(pure=true)
public <R> Set<R> uniq(SerializableFunction<X,R> mapper)
 throws Exception
```
 Gets all unique values of the results provided by a given mapper function.
 This is a shorthand for `.map(mapper).uniq()`.
 
 Type Parameters:
 
 R - the type that is returned by the `mapper` function
 
 Parameters:
 
 mapper - function that returns some values
 
 Returns:
 
 a set of distinct values returned by the `mapper` function
 
 Throws:
 
 Exception
 - countUniq
```
@Contract(pure=true)
public Integer countUniq()
 throws Exception
```
 Counts all unique values of the results.
 For example, this can be used together with the OSMContributionView to get the number of unique users editing specific feature types.
 
 Returns:
 
 the set of distinct values
 
 Throws:
 
 Exception
 - average
```
@Contract(pure=true)
public Double average()
 throws Exception
```
 Calculates the averages of the results.
 The current data values need to be numeric (castable to "Number" type), otherwise a runtime exception will be thrown.
 
 Returns:
 
 the average of the current data
 
 Throws:
 
 UnsupportedOperationException - if the data cannot be cast to numbers
 
 Exception
 - average
```
@Contract(pure=true)
public <R extends Number> Double average(SerializableFunction<X,R> mapper)
 throws Exception
```
 Calculates the average of the results provided by a given `mapper` function.
 
 Type Parameters:
 
 R - the numeric type that is returned by the `mapper` function
 
 Parameters:
 
 mapper - function that returns the numbers to average
 
 Returns:
 
 the average of the numbers returned by the `mapper` function
 
 Throws:
 
 Exception
 - weightedAverage
```
@Contract(pure=true)
public Double weightedAverage(SerializableFunction<X,WeightedValue> mapper)
 throws Exception
```
 Calculates the weighted average of the results provided by the `mapper` function.
 The mapper must return an object of the type `WeightedValue` which contains a numeric value associated with a (floating point) weight.
 
 Parameters:
 
 mapper - function that gets called for each entity snapshot or modification, needs to return the value and weight combination of numbers to average
 
 Returns:
 
 the weighted average of the numbers returned by the `mapper` function
 
 Throws:
 
 Exception
 - estimatedMedian
```
@Contract(pure=true)
public Double estimatedMedian()
 throws Exception
```
 Returns an estimate of the median of the results.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Returns:
 
 estimated median
 
 Throws:
 
 Exception
 - estimatedMedian
```
@Contract(pure=true)
public <R extends Number> Double estimatedMedian(SerializableFunction<X,R> mapper)
 throws Exception
```
 Returns an estimate of the median of the results after applying the given map function.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Parameters:
 
 mapper - function that returns the numbers to generate the mean for
 
 Returns:
 
 estimated median
 
 Throws:
 
 Exception
 - estimatedQuantile
```
@Contract(pure=true)
public Double estimatedQuantile(double q)
 throws Exception
```
 Returns an estimate of a requested quantile of the results.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Parameters:
 
 q - the desired quantile to calculate (as a number between 0 and 1)
 
 Returns:
 
 estimated quantile boundary
 
 Throws:
 
 Exception
 - estimatedQuantile
```
@Contract(pure=true)
public <R extends Number> Double estimatedQuantile(SerializableFunction<X,R> mapper,
 double q)
 throws Exception
```
 Returns an estimate of a requested quantile of the results after applying the given map function.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Parameters:
 
 mapper - function that returns the numbers to generate the quantile for
 
 q - the desired quantile to calculate (as a number between 0 and 1)
 
 Returns:
 
 estimated quantile boundary
 
 Throws:
 
 Exception
 - estimatedQuantiles
```
@Contract(pure=true)
public List<Double> estimatedQuantiles(Iterable<Double> q)
 throws Exception
```
 Returns an estimate of the quantiles of the results.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Parameters:
 
 q - the desired quantiles to calculate (as a collection of numbers between 0 and 1)
 
 Returns:
 
 estimated quantile boundaries
 
 Throws:
 
 Exception
 - estimatedQuantiles
```
@Contract(pure=true)
public <R extends Number> List<Double> estimatedQuantiles(SerializableFunction<X,R> mapper,
 Iterable<Double> q)
 throws Exception
```
 Returns an estimate of the quantiles of the results after applying the given map function.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Parameters:
 
 mapper - function that returns the numbers to generate the quantiles for
 
 q - the desired quantiles to calculate (as a collection of numbers between 0 and 1)
 
 Returns:
 
 estimated quantile boundaries
 
 Throws:
 
 Exception
 - estimatedQuantiles
```
@Contract(pure=true)
public DoubleUnaryOperator estimatedQuantiles()
 throws Exception
```
 Returns a function that computes estimates of arbitrary quantiles of the results.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Returns:
 
 a function that computes estimated quantile boundaries
 
 Throws:
 
 Exception
 - estimatedQuantiles
```
@Contract(pure=true)
public <R extends Number> DoubleUnaryOperator estimatedQuantiles(SerializableFunction<X,R> mapper)
 throws Exception
```
 Returns a function that computes estimates of arbitrary quantiles of the results after applying the given map function.
 Uses the t-digest algorithm to calculate estimates for the quantiles in a map-reduce system: https://raw.githubusercontent.com/tdunning/t-digest/master/docs/t-digest-paper/histo.pdf
 
 Parameters:
 
 mapper - function that returns the numbers to generate the quantiles for
 
 Returns:
 
 a function that computes estimated quantile boundaries
 
 Throws:
 
 Exception
 - forEach
```
@Deprecated
public void forEach(SerializableConsumer<X> action)
 throws Exception
```
 Deprecated. only for testing purposes, use `.stream().forEach()` instead
 
 Iterates over each entity snapshot or contribution, and performs a single `action` on each one of them.
 This method can be handy for testing purposes. But note that since the `action` doesn't produce a return value, it must facilitate its own way of producing output.
 
 If you'd like to use such a "forEach" in a non-test use case, use `.stream().forEach()` instead.
 
 Parameters:
 
 action - function that gets called for each transformed data entry
 
 Throws:
 
 Exception
 - collect
```
@Contract(pure=true)
public List<X> collect()
 throws Exception
```
 Collects all results into a List.
 
 Returns:
 
 a list with all results returned by the `mapper` function
 
 Throws:
 
 Exception
 - stream
```
@Contract(pure=true)
public Stream<X> stream()
 throws Exception
```
 Returns all results as a Stream.
 If the used oshdb database backend doesn't implement the stream operation directly, this will fall back to executing `.collect().stream()` instead, which buffers all results in memory first before returning them as a stream.
 
 Returns:
 
 a stream with all results returned by the `mapper` function
 
 Throws:
 
 Exception
 - mapStreamCellsOSMContribution
```
protected Stream<X> mapStreamCellsOSMContribution(SerializableFunction<OSMContribution,X> mapper)
 throws Exception
```
 Throws:
 
 Exception
 - flatMapStreamCellsOSMContributionGroupedById
```
protected Stream<X> flatMapStreamCellsOSMContributionGroupedById(SerializableFunction<List<OSMContribution>,Iterable<X>> mapper)
 throws Exception
```
 Throws:
 
 Exception
 - mapStreamCellsOSMEntitySnapshot
```
protected Stream<X> mapStreamCellsOSMEntitySnapshot(SerializableFunction<OSMEntitySnapshot,X> mapper)
 throws Exception
```
 Throws:
 
 Exception
 - flatMapStreamCellsOSMEntitySnapshotGroupedById
```
protected Stream<X> flatMapStreamCellsOSMEntitySnapshotGroupedById(SerializableFunction<List<OSMEntitySnapshot>,Iterable<X>> mapper)
 throws Exception
```
 Throws:
 
 Exception
 - mapReduceCellsOSMContribution
```
protected <R,S> S mapReduceCellsOSMContribution(SerializableFunction<OSMContribution,R> mapper,
 SerializableSupplier<S> identitySupplier,
 SerializableBiFunction<S,R,S> accumulator,
 SerializableBinaryOperator<S> combiner)
 throws Exception
```
 Generic map-reduce used by the `OSMContributionView`.
 The combination of the used types and identity/reducer functions must make "mathematical" sense:
 - the accumulator and combiner functions need to be associative,
 - values generated by the identitySupplier factory must be an identity for the combiner function: `combiner(identitySupplier(),x)` must be equal to `x`,
 - the combiner function must be compatible with the accumulator function: `combiner(u, accumulator(identitySupplier(), t)) == accumulator.apply(u, t)`
 Functionally, this interface is similar to Java8 Stream's reduce(identity,accumulator,combiner) interface.
 Type Parameters:
 
 R - the data type returned by the `mapper` function
 
 S - the data type used to contain the "reduced" (intermediate and final) results
 
 Parameters:
 
 mapper - a function that's called for each `OSMContribution`
 
 identitySupplier - a factory function that returns a new starting value to reduce results into (e.g. when summing values, one needs to start at zero)
 
 accumulator - a function that takes a result from the `mapper` function (type <R>) and an accumulation value (type <S>, e.g. the result of `identitySupplier()`) and returns the "sum" of the two; contrary to `combiner`, this function is allowed to alter (mutate) the state of the accumulation value (e.g. directly adding new values to an existing Set object)
 
 combiner - a function that calculates the "sum" of two <S> values; this function must be pure (have no side effects), and is not allowed to alter the state of the two input objects it gets!
 
 Returns:
 
 the result of the map-reduce operation, the final result of the last call to the `combiner` function, after all `mapper` results have been aggregated (in the `accumulator` and `combiner` steps)
 
 Throws:
 
 Exception
 - flatMapReduceCellsOSMContributionGroupedById
```
protected <R,S> S flatMapReduceCellsOSMContributionGroupedById(SerializableFunction<List<OSMContribution>,Iterable<R>> mapper,
 SerializableSupplier<S> identitySupplier,
 SerializableBiFunction<S,R,S> accumulator,
 SerializableBinaryOperator<S> combiner)
 throws Exception
```
 Generic "flat" version of the map-reduce used by the `OSMContributionView`, with by-osm-id grouped input to the `mapper` function.
 Contrary to the "normal" map-reduce, the "flat" version adds the possibility to return any number of results in the `mapper` function. Additionally, this interface provides the `mapper` function with a list of all `OSMContribution`s of a particular OSM entity. This is used to do more complex analyses that require the full edit history of the respective OSM entities as input.
 
 The combination of the used types and identity/reducer functions must make "mathematical" sense:
 - the accumulator and combiner functions need to be associative,
 - values generated by the identitySupplier factory must be an identity for the combiner function: `combiner(identitySupplier(),x)` must be equal to `x`,
 - the combiner function must be compatible with the accumulator function: `combiner(u, accumulator(identitySupplier(), t)) == accumulator.apply(u, t)`
 Functionally, this interface is similar to Java8 Stream's reduce(identity,accumulator,combiner) interface.
 Type Parameters:
 
 R - the data type returned by the `mapper` function
 
 S - the data type used to contain the "reduced" (intermediate and final) results
 
 Parameters:
 
 mapper - a function that's called for all `OSMContribution`s of a particular OSM entity; returns a list of results (which can have any number of entries).
 
 identitySupplier - a factory function that returns a new starting value to reduce results into (e.g. when summing values, one needs to start at zero)
 
 accumulator - a function that takes a result from the `mapper` function (type <R>) and an accumulation value (type <S>, e.g. the result of `identitySupplier()`) and returns the "sum" of the two; contrary to `combiner`, this function is allowed to alter (mutate) the state of the accumulation value (e.g. directly adding new values to an existing Set object)
 
 combiner - a function that calculates the "sum" of two <S> values; this function must be pure (have no side effects), and is not allowed to alter the state of the two input objects it gets!
 
 Returns:
 
 the result of the map-reduce operation, the final result of the last call to the `combiner` function, after all `mapper` results have been aggregated (in the `accumulator` and `combiner` steps)
 
 Throws:
 
 Exception
 - mapReduceCellsOSMEntitySnapshot
```
protected <R,S> S mapReduceCellsOSMEntitySnapshot(SerializableFunction<OSMEntitySnapshot,R> mapper,
 SerializableSupplier<S> identitySupplier,
 SerializableBiFunction<S,R,S> accumulator,
 SerializableBinaryOperator<S> combiner)
 throws Exception
```
 Generic map-reduce used by the `OSMEntitySnapshotView`.
 The combination of the used types and identity/reducer functions must make "mathematical" sense:
 - the accumulator and combiner functions need to be associative,
 - values generated by the identitySupplier factory must be an identity for the combiner function: `combiner(identitySupplier(),x)` must be equal to `x`,
 - the combiner function must be compatible with the accumulator function: `combiner(u, accumulator(identitySupplier(), t)) == accumulator.apply(u, t)`
 Functionally, this interface is similar to Java8 Stream's reduce(identity,accumulator,combiner) interface.
 Type Parameters:
 
 R - the data type returned by the `mapper` function
 
 S - the data type used to contain the "reduced" (intermediate and final) results
 
 Parameters:
 
 mapper - a function that's called for each `OSMEntitySnapshot`
 
 identitySupplier - a factory function that returns a new starting value to reduce results into (e.g. when summing values, one needs to start at zero)
 
 accumulator - a function that takes a result from the `mapper` function (type <R>) and an accumulation value (type <S>, e.g. the result of `identitySupplier()`) and returns the "sum" of the two; contrary to `combiner`, this function is allowed to alter (mutate) the state of the accumulation value (e.g. directly adding new values to an existing Set object)
 
 combiner - a function that calculates the "sum" of two <S> values; this function must be pure (have no side effects), and is not allowed to alter the state of the two input objects it gets!
 
 Returns:
 
 the result of the map-reduce operation, the final result of the last call to the `combiner` function, after all `mapper` results have been aggregated (in the `accumulator` and `combiner` steps)
 
 Throws:
 
 Exception
 - flatMapReduceCellsOSMEntitySnapshotGroupedById
```
protected <R,S> S flatMapReduceCellsOSMEntitySnapshotGroupedById(SerializableFunction<List<OSMEntitySnapshot>,Iterable<R>> mapper,
 SerializableSupplier<S> identitySupplier,
 SerializableBiFunction<S,R,S> accumulator,
 SerializableBinaryOperator<S> combiner)
 throws Exception
```
 Generic "flat" version of the map-reduce used by the `OSMEntitySnapshotView`, with by-osm-id grouped input to the `mapper` function.
 Contrary to the "normal" map-reduce, the "flat" version adds the possibility to return any number of results in the `mapper` function. Additionally, this interface provides the `mapper` function with a list of all `OSMContribution`s of a particular OSM entity. This is used to do more complex analyses that require the full list of snapshots of the respective OSM entities as input.
 
 The combination of the used types and identity/reducer functions must make "mathematical" sense:
 - the accumulator and combiner functions need to be associative,
 - values generated by the identitySupplier factory must be an identity for the combiner function: `combiner(identitySupplier(),x)` must be equal to `x`,
 - the combiner function must be compatible with the accumulator function: `combiner(u, accumulator(identitySupplier(), t)) == accumulator.apply(u, t)`
 Functionally, this interface is similar to Java8 Stream's reduce(identity,accumulator,combiner) interface.
 Type Parameters:
 
 R - the data type returned by the `mapper` function
 
 S - the data type used to contain the "reduced" (intermediate and final) results
 
 Parameters:
 
 mapper - a function that's called for all `OSMEntitySnapshot`s of a particular OSM entity; returns a list of results (which can have any number of entries)
 
 identitySupplier - a factory function that returns a new starting value to reduce results into (e.g. when summing values, one needs to start at zero)
 
 accumulator - a function that takes a result from the `mapper` function (type <R>) and an accumulation value (type <S>, e.g. the result of `identitySupplier()`) and returns the "sum" of the two; contrary to `combiner`, this function is allowed to alter (mutate) the state of the accumulation value (e.g. directly adding new values to an existing Set object)
 
 combiner - a function that calculates the "sum" of two <S> values; this function must be pure (have no side effects), and is not allowed to alter the state of the two input objects it gets!
 
 Returns:
 
 the result of the map-reduce operation, the final result of the last call to the `combiner` function, after all `mapper` results have been aggregated (in the `accumulator` and `combiner` steps)
 
 Throws:
 
 Exception
 - getTagInterpreter
```
protected TagInterpreter getTagInterpreter()
 throws org.json.simple.parser.ParseException,
 SQLException,
 IOException
```
 Throws:
 
 org.json.simple.parser.ParseException
 
 SQLException
 
 IOException
 - getTagTranslator
```
protected TagTranslator getTagTranslator()
```
 - getPreFilter
```
protected CellIterator.OSHEntityFilter getPreFilter()
```
 - getFilter
```
protected CellIterator.OSMEntityFilter getFilter()
```
 - getCellIdRanges
```
protected Iterable<XYGridTree.CellIdRange> getCellIdRanges()
```
 - getPolyFilter
```
protected  P getPolyFilter()
```
 - osmType
```
public M osmType(OSMType type1,
 OSMType... otherTypes)
```
 Limits the analysis to the given osm entity types.
 
 Parameters:
 
 type1 - the set of osm types to filter (e.g. `OSMType.NODE`)
 
 otherTypes - more osm types which should be analyzed
 
 Returns:
 
 `this` mapReducer (can be used to chain multiple commands together)
 - osmTypes
```
@Deprecated
public M osmTypes(EnumSet<OSMType> typeFilter)
```
 Deprecated. replaced by osmType(OSMType, OSMType...)
 
 deprecated.
 - osmTypes
```
@Deprecated
public M osmTypes(OSMType type1,
 OSMType... otherTypes)
```
 Deprecated. replaced by osmType(OSMType, OSMType...)
 
 deprecated.
 - where
```
@Deprecated
public M where(SerializablePredicate<OSMEntity> f)
```
 Deprecated. replaced by osmEntityFilter(org.heigit.bigspatialdata.oshdb.api.generic.function.SerializablePredicate<org.heigit.bigspatialdata.oshdb.osm.OSMEntity>)
 
 deprecated.
 - where
```
@Deprecated
public M where(OSMTagKey key)
```
 Deprecated. replaced by osmTag(OSMTagInterface)
 
 deprecated.
 - where
```
@Deprecated
public M where(String key)
```
 Deprecated. replaced by osmTag(String)
 
 deprecated.
 - where
```
@Deprecated
public M where(OSMTag tag)
```
 Deprecated. replaced by osmTag(OSMTagInterface)
 
 deprecated.
 - where
```
@Deprecated
public M where(String key,
 String value)
```
 Deprecated. replaced by osmTag(String, String)
 
 deprecated.
 - where
```
@Deprecated
public M where(String key,
 Collection<String> values)
```
 Deprecated. replaced by osmTag(String, Collection)
 
 deprecated.
 - where
```
@Deprecated
public M where(String key,
 Pattern valuePattern)
```
 Deprecated. replaced by osmTag(String, Pattern)
 
 deprecated.
 - where
```
@Deprecated
public M where(Collection<OSMTag> keyValuePairs)
```
 Deprecated. replaced by osmTag(Collection)
 
 deprecated.

Class MapReducer<X>

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

oshdb

keytables

timeout

tstamps

bboxFilter

typeFilter

Constructor Detail

MapReducer

MapReducer

Method Detail

isCancelable

copy

keytables

tagInterpreter

areaOfInterest

areaOfInterest

timestamps

timestamps

timestamps

timestamps

timestamps

osmType

osmEntityFilter

osmTag

osmTag

osmTag

osmTag

osmTag

osmTag

map

flatMap

filter

groupByEntity

aggregateBy

aggregateBy

aggregateByTimestamp

aggregateByTimestamp

aggregateByGeometry

reduce

reduce

sum

sum

count

uniq

uniq

countUniq

average

average

weightedAverage

estimatedMedian

estimatedMedian

estimatedQuantile

estimatedQuantile

estimatedQuantiles

estimatedQuantiles

estimatedQuantiles

estimatedQuantiles

forEach

collect

stream

mapStreamCellsOSMContribution

flatMapStreamCellsOSMContributionGroupedById

mapStreamCellsOSMEntitySnapshot

flatMapStreamCellsOSMEntitySnapshotGroupedById

mapReduceCellsOSMContribution

flatMapReduceCellsOSMContributionGroupedById

mapReduceCellsOSMEntitySnapshot

flatMapReduceCellsOSMEntitySnapshotGroupedById

getTagInterpreter

getTagTranslator

getPreFilter

getFilter

getCellIdRanges

getPolyFilter