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## org.apache.lucene.search.grouping.function
Class FunctionFirstPassGroupingCollector

    java.lang.Object
      org.apache.lucene.search.Collector
          org.apache.lucene.search.grouping.AbstractFirstPassGroupingCollector<MutableValue>
              org.apache.lucene.search.grouping.function.FunctionFirstPassGroupingCollector

    public class FunctionFirstPassGroupingCollector

extends AbstractFirstPassGroupingCollector<MutableValue>

Concrete implementation of `AbstractFirstPassGroupingCollector` that groups based on `ValueSource` instances.

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

Field Summary

Fields inherited from class org.apache.lucene.search.grouping.AbstractFirstPassGroupingCollector
`orderedGroups`

Constructor Summary
`FunctionFirstPassGroupingCollector(ValueSource groupByVS, Map<?,?> vsContext, Sort groupSort, int topNGroups)` Creates a first pass collector.

Method Summary
`protected MutableValue` | `copyDocGroupValue(MutableValue groupValue, MutableValue reuse)` Returns a copy of the specified group value by creating a new instance and copying the value from the specified groupValue in the new instance.
`protected MutableValue` | `getDocGroupValue(int doc)` Returns the group value for the specified doc.
`void` | `setNextReader(AtomicReaderContext readerContext)`

Methods inherited from class org.apache.lucene.search.grouping.AbstractFirstPassGroupingCollector
`acceptsDocsOutOfOrder, collect, getTopGroups, setScorer`

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

Constructor Detail

### FunctionFirstPassGroupingCollector

    public FunctionFirstPassGroupingCollector(ValueSource groupByVS,
                                              Map<?,?> vsContext,
                                              Sort groupSort,
                                              int topNGroups)
                                       throws IOException

  Creates a first pass collector.

  Parameters:
    `groupByVS` - The `ValueSource` instance to group by
    `vsContext` - The ValueSource context
    `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.
  Throws:
    `IOException` - When I/O related errors occur

Method Detail

### getDocGroupValue

    protected MutableValue getDocGroupValue(int doc)

  Description copied from class: `AbstractFirstPassGroupingCollector`
  Returns the group value for the specified doc.

  Specified by:
    `getDocGroupValue` in class `AbstractFirstPassGroupingCollector<MutableValue>`
  Parameters:
    `doc` - The specified doc
  Returns:
    the group value for the specified doc

### copyDocGroupValue

    protected MutableValue copyDocGroupValue(MutableValue groupValue,
                                             MutableValue reuse)

  Description copied from class: `AbstractFirstPassGroupingCollector`
  Returns a copy of the specified group value by creating a new instance and copying the value from the specified groupValue in the new instance. Or optionally the reuse argument can be used to copy the group value in.

  Specified by:
    `copyDocGroupValue` in class `AbstractFirstPassGroupingCollector<MutableValue>`
  Parameters:
    `groupValue` - The group value to copy
    `reuse` - Optionally a reuse instance to prevent a new instance creation
  Returns:
    a copy of the specified group value

### setNextReader

    public void setNextReader(AtomicReaderContext readerContext)
                       throws IOException

  Overrides:
    `setNextReader` in class `AbstractFirstPassGroupingCollector<MutableValue>`
  Throws:
    `IOException`

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