How to calculate combination and permutation in R?

Question

How one can calculate the number of combinations and permutations in R?

The Combinations package failed to install on Linux with the following message:

> install.packages("Combinations")
Installing package(s) into ‘/home/maxim/R/x86_64-pc-linux-gnu-library/2.13’
(as ‘lib’ is unspecified)
Warning message:
In getDependencies(pkgs, dependencies, available, lib) :
  package ‘Combinations’ is not available (for R version 2.13.1)

Solution 1

You can use the combinat package with R 2.13:

install.packages("combinat")
require(combinat)
permn(3)
combn(3, 2)

If you want to know the number of combination/permutations, then check the size of the result, e.g.:

length(permn(3))
dim(combn(3,2))[2]

Solution 2

The function combn is in the standard utils package (i.e. already installed)

choose is also already available in the Special {base}

Solution 3

If you don't want your code to depend on other packages, you can always just write these functions:

perm = function(n, x) {
  factorial(n) / factorial(n-x)
}

comb = function(n, x) {
  factorial(n) / factorial(n-x) / factorial(x)
}

Solution 4

The Combinations package is not part of the standard CRAN set of packages, but is rather part of a different repository, omegahat. To install it you need to use

install.packages("Combinations", repos = "http://www.omegahat.org/R")

See the documentation at http://www.omegahat.org/Combinations/

Solution 5

It might be that the package "Combinations" is not updated anymore and does not work with a recent version of R (I was also unable to install it on R 2.13.1 on windows). The package "combinat" installs without problem for me and might be a solution for you depending on what exactly you're trying to do.

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Comments

[Maxim Veksler]

Is there something that could just give me a number of possible combinations, rather then printing them all?

[Maxim Veksler]

This also does not work, I think that the R version I'm using is (2.13) is not compatible

[Brian Diggs]

Ah, there was a typo; it should be omegahat, not omeghat. I copied and pasted the command, but I should have tested it first. I've updated my answer. This updated code works for me in 2.13.2 on Windows.

[chl]

@MaximVeksler Take a look at choose. (choose(5, 2) == ncol(combn(5, 2)))

[bubakazouba]

wow alot of hassle for a simple question that its answer was 3 words "the choose function"

[Asif Iqbal]

This site can be used as alternate: englishact.com/Permutation/index.php

[Marius Hofert]

That's a bad idea numerically. R can evaluate choose(500, 2) but not factorial(500). You should at least work with lfactorial and then take exp(). The only reason I'm posting this is that your answer has so many upvotes, it seems people don't know these things...

[agent18]

choose(n,k) = nCk