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From "Dongjoon Hyun (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SPARK-15660) RDD and Dataset should show the consistent value for variance/stdev.
Date Tue, 31 May 2016 05:22:12 GMT
Dongjoon Hyun created SPARK-15660:
-------------------------------------

             Summary: RDD and Dataset should show the consistent value for variance/stdev.
                 Key: SPARK-15660
                 URL: https://issues.apache.org/jira/browse/SPARK-15660
             Project: Spark
          Issue Type: Bug
          Components: Spark Core
            Reporter: Dongjoon Hyun


In Spark-11490, `variance/stdev` are redefined as the **sample** `variance/stdev` instead
of population ones.

This issue addresses the only remaining legacy in RDD. This may cause breaking changes, but
we had better be consistent in Spark 2.0 if possible.
{code}
scala> val rdd = sc.parallelize(Seq(1.0, 2.0, 3.0))
rdd: org.apache.spark.rdd.RDD[Double] = ParallelCollectionRDD[0] at parallelize at <console>:24

scala> rdd.stdev
res0: Double = 0.816496580927726                                                

scala> rdd.toDS().describe().show()
16/05/30 22:20:12 WARN ObjectStore: Version information not found in metastore. hive.metastore.schema.verification
is not enabled so recording the schema version 1.2.0
16/05/30 22:20:12 WARN ObjectStore: Failed to get database default, returning NoSuchObjectException
+-------+-----+
|summary|value|
+-------+-----+
|  count|    3|
|   mean|  2.0|
| stddev|  1.0|
|    min|  1.0|
|    max|  3.0|
+-------+-----+
{code}



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