[R] code to find all distinct subsets of size r from a set of size n

[David Winsemius]

If your subsets are to be taken from the rows of a dataframe, df, and  
the size is r, then something like this could satisfy:

apply(combn(nrow(df), r), 2, function(x) df[x, ])

(Although these are not really permutations as I understand that term.)

-- 
David Winsemius

On Mar 13, 2009, at 8:35 AM, Dale Steele wrote:

> I'm doing a permutation test and need to efficiently generate all
> distinct subsets of size r from a set of size n.  P 138 of MASS (4th
> ed) notes that  "The code to generate this efficiently is in the
> scripts".  I was unable to find this code on quick inspection of the
> \library\MASS\scripts file for Chapter 5 and 'subsets' is not a
> function in MASS.
>
> I did find this problem is discussed in RNews, Programmer's Niche
> 1(1):27 - 30 and RNews, 1(2):29-31.  Is there function in 'base'  R or
> other package to do this?  Thanks.  --Dale
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT