<td> <b>groupByKey</b>([<i>numTasks</i>]) </td>

<td> When called on a dataset of (K, V) pairs, returns a dataset of (K, Seq[V]) pairs. <br />

<b>Note:</b> By default, if the RDD already has a partitioner, the task number is decided by the partition number of the partitioner, or else relies on the value of <code>spark.default.parallelism</code> if the property is set , otherwise depends on the partition number of the RDD. You can pass an optional <code>numTasks</code> argument to set a different number of tasks.

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<td> <b>reduceByKey</b>(<i>func</i>, [<i>numTasks</i>]) </td>