[R] generate combination set

[Bill.Venables at csiro.au]

There are a number of packages that do this, but here is a simple
function for choosing subsets:

subsets <- function(n, r)  {
  if(is.numeric(n) & length(n) == 1) v <- 1:n else {
    v <- n
    n <- length(v)
  }
  subs <- function(n, r, v)
    if(r <= 0) NULL else
    if(r >= n) matrix(v[1:n], nrow = 1) else
    rbind(cbind(v[1], subs(n - 1, r - 1, v[-1])),
                      subs(n - 1, r    , v[-1]))
  subs(n, r, v)
}

Here is an example of how to use it:


> set <- LETTERS[1:7]
> subsets(set, 2)
      [,1] [,2]
 [1,] "A"  "B" 
 [2,] "A"  "C" 
 [3,] "A"  "D" 
 [4,] "A"  "E" 
 [5,] "A"  "F" 
 [6,] "A"  "G" 
 [7,] "B"  "C" 
 [8,] "B"  "D" 
 [9,] "B"  "E" 
[10,] "B"  "F" 
[11,] "B"  "G" 
[12,] "C"  "D" 
[13,] "C"  "E" 
[14,] "C"  "F" 
[15,] "C"  "G" 
[16,] "D"  "E" 
[17,] "D"  "F" 
[18,] "D"  "G" 
[19,] "E"  "F" 
[20,] "E"  "G" 
[21,] "F"  "G"  


Bill Venables
CSIRO Laboratories
PO Box 120, Cleveland, 4163
AUSTRALIA
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mailto:Bill.Venables at csiro.au
http://www.cmis.csiro.au/bill.venables/ 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of aiminy at iastate.edu
Sent: Thursday, 15 November 2007 2:51 PM
To: r-help at r-project.org
Subject: [R] generate combination set

I have a set data={A,B,C,D,E,F,G}
I want to choose 2 letter from 8 letters, i.e. generate the combination
set 
for choose 2 letters from 8 letters.
I want to get the liking:
combination set={AB,AC,AD,....}
Does anyone konw how to do in R.

thanks,

Aimin

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