org.apache.lucene.facet

## Class RandomSamplingFacetsCollector

- java.lang.Object
- - org.apache.lucene.search.SimpleCollector
  - - org.apache.lucene.facet.FacetsCollector
    - - org.apache.lucene.facet.RandomSamplingFacetsCollector

- All Implemented Interfaces:
    Collector, LeafCollector

      public class RandomSamplingFacetsCollector
      extends FacetsCollector

  Collects hits for subsequent faceting, using sampling if needed. Once you've run a search and collect hits into this, instantiate one of the `Facets` subclasses to do the facet counting. Note that this collector does not collect the scores of matching docs (i.e. `FacetsCollector.MatchingDocs.scores`) is `null`.

  If you require the original set of hits, you can call `getOriginalMatchingDocs()`. Also, since the counts of the top-facets is based on the sampled set, you can amortize the counts by calling `amortizeFacetCounts(org.apache.lucene.facet.FacetResult, org.apache.lucene.facet.FacetsConfig, org.apache.lucene.search.IndexSearcher)`.

- - ### Nested Class Summary

    - ### Nested classes/interfaces inherited from class org.apache.lucene.facet.FacetsCollector

      `FacetsCollector.MatchingDocs`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `RandomSamplingFacetsCollector(int sampleSize)` Constructor with the given sample size and default seed.
    `RandomSamplingFacetsCollector(int sampleSize, long seed)` Constructor with the given sample size and seed.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `FacetResult` | `amortizeFacetCounts(FacetResult res, FacetsConfig config, IndexSearcher searcher)` Note: if you use a counting `Facets` implementation, you can amortize the sampled counts by calling this method.
    `List<FacetsCollector.MatchingDocs>` | `getMatchingDocs()` Returns the sampled list of the matching documents.
    `List<FacetsCollector.MatchingDocs>` | `getOriginalMatchingDocs()` Returns the original matching documents.
    `double` | `getSamplingRate()` Returns the sampling rate that was used.

    - ### Methods inherited from class org.apache.lucene.facet.FacetsCollector

      `collect, doSetNextReader, getKeepScores, needsScores, search, search, search, searchAfter, searchAfter, searchAfter, setScorer`

    - ### 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`

    - ### Methods inherited from interface org.apache.lucene.search.Collector

      `getLeafCollector`

- - ### Constructor Detail

    - #### RandomSamplingFacetsCollector

          public RandomSamplingFacetsCollector(int sampleSize)

      Constructor with the given sample size and default seed.
      See Also:
        `RandomSamplingFacetsCollector(int, long)`

    - #### RandomSamplingFacetsCollector

          public RandomSamplingFacetsCollector(int sampleSize,
                                               long seed)

      Constructor with the given sample size and seed.
      Parameters:
        `sampleSize` - The preferred sample size. If the number of hits is greater than the size, sampling will be done using a sample ratio of sampling size / totalN. For example: 1000 hits, sample size = 10 results in samplingRatio of 0.01. If the number of hits is lower, no sampling is done at all
        `seed` - The random seed. If `0` then a seed will be chosen for you.

  - ### Method Detail

    - #### getMatchingDocs

          public List<FacetsCollector.MatchingDocs> getMatchingDocs()

      Returns the sampled list of the matching documents. Note that a `FacetsCollector.MatchingDocs` instance is returned per segment, even if no hits from that segment are included in the sampled set.

      Note: One or more of the MatchingDocs might be empty (not containing any hits) as result of sampling.

      Note: `MatchingDocs.totalHits` is copied from the original MatchingDocs, scores is set to `null`

      Overrides:
        `getMatchingDocs` in class `FacetsCollector`

    - #### getOriginalMatchingDocs

          public List<FacetsCollector.MatchingDocs> getOriginalMatchingDocs()

      Returns the original matching documents.

    - #### amortizeFacetCounts

          public FacetResult amortizeFacetCounts(FacetResult res,
                                                 FacetsConfig config,
                                                 IndexSearcher searcher)
                                          throws IOException

      Note: if you use a counting `Facets` implementation, you can amortize the sampled counts by calling this method. Uses the `FacetsConfig` and the `IndexSearcher` to determine the upper bound for each facet value.
      Throws:
        `IOException`

    - #### getSamplingRate

          public double getSamplingRate()

      Returns the sampling rate that was used.

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