How to get data from a specific partition in Spark

问题:

I want to access data from a particular partition in Spark RDD. I can get address of a partition as follow:

myRDD.partitions(0)

But I want to get data from myRDD.partitions(0) partition. I tried official org.apache.spark documentation but couldn't find.

Thanks in advance.

回答1:

You can use mapPartitionsWithIndex as follows

// Create (1, 1), (2, 2), ..., (100, 100) dataset
// and partition by key so we know what to expect
val rdd = sc.parallelize((1 to 100) map (i => (i, i)), 16)
  .partitionBy(new org.apache.spark.HashPartitioner(8))

val zeroth = rdd
  // If partition number is not zero ignore data
  .mapPartitionsWithIndex((idx, iter) => if (idx == 0) iter else Iterator())

// Check if we get expected results 8, 16, ..., 96
assert (zeroth.keys.map(_ % 8 == 0).reduce(_ & _) & zeroth.count == 12)