[R] combinations

[Michaell Taylor]

I need to construct all possible combinations of an vector of length N taken
X at a time for simulation purposes.  Taking a a small vector as an example:


>input <- c('a','b','c','d')
>somefunction(input)
a,b,c
a,b,d
a,c,d
b,c,d

my only solution thus far is:

somefunction <- function(x){
      ...a series of grotesque and horribly inefficient loops
      deleted to save face.
      }

For my purposes, N=20 and X=5, meaning there are about 15k combinations.

I assumed this might be a common problem, but I am coming up empty on my searches
of the usual suspect web sites.

Thanks in advance for any pointers anyone may have.

Michaell
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