Dear Friends,

I have a matrix of size 5000 X 20. The first two columns are indicator variables taking the value of either 0 or 1. Let us call the first two columns Y1 and Y2. 

I need to randomly sample 1000 rows with all the associated columns, in other words my new matrix should be of size 1000 X 20. I realize that using this command

 newmat <- mainmat[sample(1000,replace=F),]

achieves this. However, I would like to make sure that both Y1 and Y2 have more or less an equal amount of 0's and 1's. At present when I sample, I get cases where sometimes all my Y2's are 0. Is there any way to accomodate this problem.

Thanks in advance.

Regards

Anup

       
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