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
Seeking help on permutation
2 messages · Megh Dal, 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/