[R] Random Sampling from a Matrix
ligges at statistik.uni-dortmund.de
Wed Aug 22 10:05:54 CEST 2007
Anup Nandialath wrote:
> 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.
Yes, for example drawing samples stratified by the values of Y1 or Y2.
> Thanks in advance.
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