org.apache.lucene.search.grouping

Class BlockGroupingCollector

java.lang.Object

org.apache.lucene.search.SimpleCollector

org.apache.lucene.search.grouping.BlockGroupingCollector

All Implemented Interfaces:

Collector, LeafCollector

public class BlockGroupingCollector
extends SimpleCollector

BlockGroupingCollector performs grouping with a single pass collector, as long as you are grouping by a doc block field, ie all documents sharing a given group value were indexed as a doc block using the atomic IndexWriter.addDocuments() or IndexWriter.updateDocuments() API.

This results in faster performance (~25% faster QPS) than the two-pass grouping collectors, with the tradeoff being that the documents in each group must always be indexed as a block. This collector also fills in TopGroups.totalGroupCount without requiring the separate TermAllGroupsCollector. However, this collector does not fill in the groupValue of each group; this field will always be null.

NOTE: this collector makes no effort to verify the docs were in fact indexed as a block, so it's up to you to ensure this was the case.

See org.apache.lucene.search.grouping for more details including a full code example.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Constructor Summary

Constructors

Constructor and Description
BlockGroupingCollector(Sort groupSort, int topNGroups, boolean needsScores, Weight lastDocPerGroup) Create the single pass collector.

Method Summary

Methods

Modifier and Type	Method and Description
void	collect(int doc)
protected void	doSetNextReader(LeafReaderContext readerContext)
TopGroups<?>	getTopGroups(Sort withinGroupSort, int groupOffset, int withinGroupOffset, int maxDocsPerGroup, boolean fillSortFields) Returns the grouped results.
boolean	needsScores()
void	setScorer(Scorer scorer)

Methods inherited from class org.apache.lucene.search.SimpleCollector

getLeafCollector

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BlockGroupingCollector

public BlockGroupingCollector(Sort groupSort,
                      int topNGroups,
                      boolean needsScores,
                      Weight lastDocPerGroup)
                       throws IOException

Create the single pass collector.

Parameters:

groupSort - The Sort used to sort the groups. The top sorted document within each group according to groupSort, determines how that group sorts against other groups. This must be non-null, ie, if you want to groupSort by relevance use Sort.RELEVANCE.

topNGroups - How many top groups to keep.

needsScores - true if the collected documents require scores, either because relevance is included in the withinGroupSort or because you plan to pass true for either getSscores or getMaxScores to getTopGroups(org.apache.lucene.search.Sort, int, int, int, boolean)

lastDocPerGroup - a Weight that marks the last document in each group.

Throws:

IOException

Method Detail

getTopGroups

public TopGroups<?> getTopGroups(Sort withinGroupSort,
                        int groupOffset,
                        int withinGroupOffset,
                        int maxDocsPerGroup,
                        boolean fillSortFields)
                          throws IOException

Returns the grouped results. Returns null if the number of groups collected is <= groupOffset.

NOTE: This collector is unable to compute the groupValue per group so it will always be null. This is normally not a problem, as you can obtain the value just like you obtain other values for each matching document (eg, via stored fields, via DocValues, etc.)

Parameters:

withinGroupSort - The Sort used to sort documents within each group. Passing null is allowed, to sort by relevance.

groupOffset - Which group to start from

withinGroupOffset - Which document to start from within each group

maxDocsPerGroup - How many top documents to keep within each group.

fillSortFields - If true then the Comparable values for the sort fields will be set

Throws:

IOException

setScorer

public void setScorer(Scorer scorer)
               throws IOException

Specified by:

setScorer in interface LeafCollector

Overrides:

setScorer in class SimpleCollector

Throws:

IOException

collect

public void collect(int doc)
             throws IOException

Specified by:

collect in interface LeafCollector

Specified by:

collect in class SimpleCollector

Throws:

IOException

doSetNextReader

protected void doSetNextReader(LeafReaderContext readerContext)
                        throws IOException

Overrides:

doSetNextReader in class SimpleCollector

Throws:

IOException

needsScores

public boolean needsScores()