Hi everyone,
I have a large RDD and I am trying to create a RDD of a random sample of
pairs of elements from this RDD. The elements composing a pair should come
from the same partition for efficiency. The idea I've come up with is to
take two random samples and then use zipPartitions to pair each i-th element
of the first sample with the i-th element of the second sample. Here is a
sample code illustrating the idea:
-----------
val rdd = sc.parallelize(1 to 60000, 16)
val sample1 = rdd.sample(true,0.01,42)
val sample2 = rdd.sample(true,0.01,43)
def myfunc(s1: Iterator[Int], s2: Iterator[Int]): Iterator[String] =
{
var res = List[String]()
while (s1.hasNext && s2.hasNext)
{
val x = s1.next + " " + s2.next
res ::= x
}
res.iterator
}
val pairs = sample1.zipPartitions(sample2)(myfunc)
-------------
However I am not happy with this solution because each element is most
likely to be paired with elements that are "closeby" in the partition. This
is because sample returns an "ordered" Iterator.
Any idea how to fix this? I did not find a way to efficiently shuffle the
random sample so far.
Thanks a lot!
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