How to loop over subsets of length k of a list of length n in R?

Question

I am given two numbers n and k with 0 < k < n. How can I loop over all possible combinations of subsets of length k?

E.g. I have x <- 1:10. Then I want to do

for (y in c(c(1,2,3), c(1,2,4), c(1,2,5), ..., c(8, 9, 10))){
   ...
}

Answer 1

You can use combn to get an array of all the subsets, then convert that into a list using asplit. Just iterate along this list.

For example, the following code will print out all the length-3 subsets of x:

x <- 1:10
n <- 10
k <- 3

subsets <- asplit(combn(n, k), 2)

for(i in subsets) {
  print(x[i])
}