Map Reduce: How can partitioning two data-sets records and how can get these blocks to make them pairs

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Java

I want to create a Map function with the following operations:

Step 1:

I have two data sets R and S. I want to partition the two data sets into n equal-sized blocks which can be done by putting every (R/n and S/n )records into one block.

After that:

Step 2: Then every possible pair of blocks (one from R and one from S) is partitioned into a bucket at the end of Map phase so that can be taken from the Reduce Function as input with some id as key for each value pairs. e.g will be

<id:(Sij,Ril)>

So my questions are:

1)Is there any implemented function that I can use for step 1? How implement this operation separately for each data-set.

2)How can I refer specifically to these data sets in step 2 so that I can take one block from R and one from S?

Note: In main I define the two data sets like this :

FileInputFormat.setInputPaths(conf, new Path(args[0]), new Path(args[1]));