[R] More efficient alternative to combn()?

elgorgonzola elgorgonzola at hotmail.com
Fri Mar 26 13:53:12 CET 2010


i am working on a problem where i need to compute the products of all
possible combinations of size m of the elements of a vector. I know that
this can be achieved using the function combn(), e.g.:

> vector <- 1:6
> combn(x = vector, m = 3, FUN = function(y) prod(y))

In my case the vector has 2000 elements and i need to compute the values
specified above for m = 32. Using combn() i encounter problems for m >= 4.
Is there any alternative to combn() that works more efficiently? Also my
vector contains many duplicates, so there are actually only about 300
distinct values in the vector. This reduces the number of possible
combinations significantly. Is there any way to use this fact to reduce the
computational cost?

Thanks in advance,

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