[jira] [Created] (SPARK-17416) Add Dataset.groupByKey overload that takes a value selector function

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

Daniel Shields created SPARK-17416:
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             Summary: Add Dataset.groupByKey overload that takes a value selector function
                 Key: SPARK-17416
                 URL: https://issues.apache.org/jira/browse/SPARK-17416
             Project: Spark
          Issue Type: New Feature
            Reporter: Daniel Shields


I propose that the following overload be added to Dataset[T]:

def groupByKey[K, V](keyFunc: T => K, valueFunc: T => V)(implicit arg0: Encoder[K], implicit arg1: Encoder[V])

This would simplify a number of use cases.  For example, consider the following classic MapReduce query:

rdd.flatMap(f).reduceByKey(g) // where f returns a list of tuples


An idiomatic way to write this with Spark 2.0 would be:

dataset.flatMap(f).groupByKey(_._1, _._2).reduceGroups(g)

Without the groupByKey overload suggested above, this must be written as:

dataset.flatMap(f).groupByKey(_._1).reduceGroups((a, b) => g(a._2, b._2))



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