Combination without repetition in R
11,369
Solution 1
Try something like:
x <- c("a","b","c","d","e")
d1 <- combn(x,3) # All combinations
d1
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
# [1,] "a" "a" "a" "a" "a" "a" "b" "b" "b" "c"
# [2,] "b" "b" "b" "c" "c" "d" "c" "c" "d" "d"
# [3,] "c" "d" "e" "d" "e" "e" "d" "e" "e" "e"
nrow(unique(t(d1))) == nrow(t(d1))
# [1] TRUE
d2 <- expand.grid(x,x,x) # All permutations
d2
# Var1 Var2 Var3
# 1 a a a
# 2 b a a
# 3 c a a
# 4 d a a
# 5 e a a
# 6 a b a
# 7 b b a
# 8 c b a
# 9 d b a
# ...
nrow(unique(d2)) == nrow(d2)
# [1] TRUE
Solution 2
try this
x <- c("a","b","c","d","e")
expand.grid(rep(list(x), 3))
Author by
Error404
Updated on June 11, 2022Comments
-
Error404 almost 2 years
I am trying to get all the possible combinations of length 3 of the elements of a variable. Although it partly worked with combn() I did not quite get the output I was looking for. Here's my example
x <- c("a","b","c","d","e") t(combn(c(x,x), 3))
The output I get looks like this
[,1] [,2] [,3] [1,] "a" "b" "c" [2,] "a" "b" "d" [3,] "a" "b" "e"
I am not really happy with this command for 2 reasons. I wanted to get an output that says "a+b+c" "a+b+b"...., unfortunately I wasn't able to edit the output with paste() or something.
I was also looking forward for one combination of each set of letters, that is I either get "a+b+c" or "b+a+c" but not both.