Hi,
Perhaps you can use expand.grid and then remove the mirror combinations,
values <- 1:3
tmp <- expand.grid(values, values)
unique.combs <- tmp[tmp[, 1]<=tmp[, 2], ]
unique.combs[do.call(order, unique.combs), ] # reorder if you wish
Var1 Var2
1 1 1
4 1 2
7 1 3
5 2 2
8 2 3
9 3 3
I vaguely recall a discussion a few months ago on extending this
approach to a variable number of arguments to expand.grid.
Hope this helps,
baptiste
On 11 Dec 2008, at 17:00, Reuben Cummings wrote:
Hi,
This has been asked before but not sufficiently answered from what I
could find. How do you create combinations
with repetitions (multisets) in R?
If I have
set <- array(1:3)
And I want to choose all combinations of picking 2 numbers, I want to
get a print out like
[,1] [,2]
[1,] 1 1
[2,] 1 2
[3,] 1 3
[4,] 2 2
[5,] 2 3
[6,] 3 3
subsets(set, 2, allow.repeat=T) should work, but I can't get the
multic package to install, t(combn(set,2)) was suggested but it
doesn't produce repetitions; expand.grid(rep(list(1:3), 2)) was also
suggested, but it produces permuations, not combinations.
Additionally, I would like to iterate through each resultant set for
large n (similar to the description for getNextSet {pcalg}). Any
suggestions?
Reuben Cummings
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_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
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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.
