combining column number having same values

Question

I have a matrix in the following form

[,1]   [,2]   [,3]   [,4]   [,5]   [,6]   [,7]   [,8]   [,9]  [,10]  [,11]
   1     1     3      2      3       1      1     2      3       3      2

and following is my desired output (combining the column numbers, having same values).

a<-1,2,6,7
b<-3,5,9,10
c<-4,8,11

Answer 1

The following gives you a list which should be enough:

aList <- setNames(split(seq_along(mat), mat), unique(letters[mat]))
aList
#  $a
# [1] 1 2 6 7
#
# $c
# [1]  4  8 11
# 
# $b
# [1]  3  5  9 10

But if you really need variables in your environment, you can then do:

attach(aList)

Answer 2

m1 <-  matrix(c(1, 1, 3, 2, 3, 1, 1, 2, 3, 3, 2), nrow = 1)
split(seq_len(ncol(m1)), m1[1, ])

gives you a list with the desired elements. I assume you don't really want to create vectors a, b and c

split(seq_len(ncol(m1)), m1[1, ])

$`1`
[1] 1 2 6 7

$`2`
[1]  4  8 11

$`3`
[1]  3  5  9 10