org.apache.lucene.search.grouping

## Class FirstPassGroupingCollector<T>

- java.lang.Object
- - org.apache.lucene.search.SimpleCollector
  - - org.apache.lucene.search.grouping.FirstPassGroupingCollector<T>

- All Implemented Interfaces:
    Collector, LeafCollector

      public class FirstPassGroupingCollector<T>
      extends SimpleCollector

  FirstPassGroupingCollector is the first of two passes necessary to collect grouped hits. This pass gathers the top N sorted groups. Groups are defined by a `GroupSelector`

  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.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected TreeSet<CollectedSearchGroup<T>>` | `orderedGroups`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `FirstPassGroupingCollector(GroupSelector<T> groupSelector, Sort groupSort, int topNGroups)` Create the first pass collector.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `collect(int doc)`
    `protected void` | `doSetNextReader(LeafReaderContext readerContext)`
    `GroupSelector<T>` | `getGroupSelector()`
    `Collection<SearchGroup<T>>` | `getTopGroups(int groupOffset, boolean fillFields)` Returns top groups, starting from offset.
    `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`

- - ### Field Detail

    - #### orderedGroups

          protected TreeSet<CollectedSearchGroup<T>> orderedGroups

      NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

  - ### Constructor Detail

    - #### FirstPassGroupingCollector

          public FirstPassGroupingCollector(GroupSelector<T> groupSelector,
                                            Sort groupSort,
                                            int topNGroups)

      Create the first pass collector.
      Parameters:
        `groupSelector` - a GroupSelector used to defined groups
        `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.

  - ### Method Detail

    - #### needsScores

          public boolean needsScores()

    - #### getTopGroups

          public Collection<SearchGroup<T>> getTopGroups(int groupOffset,
                                                         boolean fillFields)
                                                  throws IOException

      Returns top groups, starting from offset. This may return null, if no groups were collected, or if the number of unique groups collected is <= offset.
      Parameters:
        `groupOffset` - The offset in the collected groups
        `fillFields` - Whether to fill to `SearchGroup.sortValues`
      Returns:
        top groups, starting from offset
      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`

    - #### getGroupSelector

          public GroupSelector<T> getGroupSelector()

      Returns:
        the GroupSelector used for this Collector

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