[R] Seeking help on permutation

[Joshua Wiley]

Hi,

Look at ?combn

t(combn(Vector, 2))

gives:

     [,1] [,2]
[1,] "a"  "b"
[2,] "a"  "c"
[3,] "b"  "c"

No idea how it is speed-wise.

HTH,

Josh

On Fri, Jul 22, 2011 at 10:09 AM, Megh Dal <megh700004 at yahoo.com> wrote:
> Let say, I have a character vector of arbitrary length:
>
> Vector <- c("a", "b", "c")
>
> Using that vector I would like to create a matrix (with number of columns as 2) with all pairwise combinations of those elements, like:
>
> Vector <- c("a", "b", "c")
> Mat     <- rbind(c("a", "b"), c("a", "c"), c("b", "c")); Mat  # number of rows will obviously be n(n-1)/2
>      [,1] [,2]
> [1,] "a"  "b"
> [2,] "a"  "c"
> [3,] "b"  "c"
>
>
> Order must be kept same as c("c", "a") or c("c", "b") would not be allowed. Additionally, actually I have a very big initial character vector therefore I need to maintain speed as well.
>
> I would be really grateful if somebody guide me how to do that
>
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>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
https://joshuawiley.com/