How to shift each row of a matrix in R

Question

I have a matrix of this form:

a b c
d e 0
f 0 0

and I want to transform it into something like this:

a b c
0 d e
0 0 f
         


        

Answer 1

Assuming that your example is representative, i.e., you have always a triangle structure of letters and zeros:

mat <- structure(c("a", "d", "f", "b", "e", "0", "c", "0", "0"), 
                 .Dim = c(3L, 3L), .Dimnames = list(NULL, NULL))
res <- matrix(0, nrow(mat), ncol(mat))
res[lower.tri(res, diag=TRUE)] <- t(mat)[t(mat)!="0"]
t(res)
#     [,1] [,2] [,3]
# [1,] "a"  "b"  "c" 
# [2,] "0"  "d"  "e" 
# [3,] "0"  "0"  "f"