[jira] [Created] (SPARK-13600) Incorrect number of buckets in QuantileDiscretizer

["Oliver Pierson (JIRA)" <ji...@apache.org>]

Oliver Pierson created SPARK-13600:
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             Summary: Incorrect number of buckets in QuantileDiscretizer
                 Key: SPARK-13600
                 URL: https://issues.apache.org/jira/browse/SPARK-13600
             Project: Spark
          Issue Type: Bug
          Components: MLlib
    Affects Versions: 1.6.0, 2.0.0
            Reporter: Oliver Pierson


Under certain circumstances, QuantileDiscretizer fails to calculate the correct splits resulting in an incorrect number of buckets/bins.

E.g.

val df = sc.parallelize(1.0 to 10.0 by 1.0).map(Tuple1.apply).toDF("x")
val discretizer = new QuantileDiscretizer().setInputCol("x").setOutputCol("y").setNumBuckets(5)
discretizer.fit(df).getSplits

gives:
Array(-Infinity, 2.0, 4.0, 6.0, 8.0, 10.0, Infinity)
which corresponds to 6 buckets (not 5).

The problem appears to be in the QuantileDiscretizer.findSplitsCandidates method.



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