1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
|
#===========================================================================#
# caTools - R library #
# Copyright (C) 2005 Jarek Tuszynski #
# Distributed under GNU General Public License version 3 #
#===========================================================================#
combs = function(v,k) {
# combs(V,K) - finds all unordered combinations of K elements from vector V
# V is a vector of length N
# K is a integer
# combs(V,K) creates a matrix with N!/((N-K)! K!) rows
# and K columns containing all possible combinations of N elements taken K at a time.
# example: combs(1:3,2) returns matrix with following rows (1 2), (1 3), (2 3)
n = length(v)
if (n==k ) P = matrix(v,1,n)
else if (k==1 ) P = matrix(v,n,1)
else if (k==n-1) P = matrix( rep(v, each=n-1), n, n-1)
else if (k< n) {
P = matrix(0,0,k)
if (k < n & k > 1) {
for (i in 1:(n-k+1)) {
Q = combs(v[(i+1):n],k-1)
j = nrow(Q)
P = rbind(P, cbind(rep(v[i],j), Q))
}
}
} else
stop("combs: number m has to be smaller or equal to length of vector v")
return(P)
}
|