There is a set A having $N$ elements. Based on set A, I would like to construct $M$ groups, where each group has $P$ elements. Naturally, $M P <N$. All of those elements in the $M$ groups are sampled from set A by following the two criteria, they are different with each other; the sampling probability for each of these MP elements are the same.
Which kind of sampling method should I use? How to do that in R?