[R] generate combination set

[Bill.Venables at csiro.au]

Actually, (now that I know about combn), a better way is

t(matrix(set[combn(7,2)], nrow = 2))

Bill V. 

-----Original Message-----
From: Adrian Dusa [mailto:dusa.adrian at gmail.com] 
Sent: Thursday, 15 November 2007 11:55 PM
To: Venables, Bill (CMIS, Cleveland)
Cc: aiminy at iastate.edu; r-help at r-project.org
Subject: Re: [R] generate combination set

Using your "set", wouldn't it be simpler like this?

t(apply(combn(7,2), 2, function(x) set[x]))

Hth,
Adrian

On Thursday 15 November 2007, Bill.Venables at csiro.au wrote:
> 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
> Office Phone (email preferred): +61 7 3826 7251
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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
>
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



-- 
Adrian Dusa
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