R help - Jul 2011 - Seeking help on permutation

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

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
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


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