[jira] [Created] (SPARK-16961) Utils.randomizeInPlace does not shuffle arrays uniformly

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

Nicholas created SPARK-16961:
--------------------------------

             Summary: Utils.randomizeInPlace does not shuffle arrays uniformly
                 Key: SPARK-16961
                 URL: https://issues.apache.org/jira/browse/SPARK-16961
             Project: Spark
          Issue Type: Bug
          Components: Spark Core
    Affects Versions: 2.0.0
            Reporter: Nicholas
            Priority: Minor


The Utils.randomizeInPlace method, which is meant to uniformly shuffle the elements on an input array, never shuffles elements to their starting position. That is, every permutation of the input array is equally likely to be returned, except for any permutation in which any element is in the same position where it began. These permutations are never output.
This is because line 827 of Utils.scala should be
{{val j = rand.nextInt(i + 1)}}
instead of
{{val j = rand.nextInt(i)}}



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@spark.apache.org
For additional commands, e-mail: issues-help@spark.apache.org