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

A head and tail solution doesn't seem as readable as a for loop to me, and may not even be as quick. Nonetheless...

t( sapply( 0:(nrow(mat)-1) , function(x) c( tail( mat[x+1,] , x ) , head( mat[x+1,] , nrow(mat)-x ) ) ) )
#     [,1] [,2] [,3]
#[1,] "a"  "b"  "c" 
#[2,] "0"  "d"  "e" 
#[3,] "0"  "0"  "f" 

A for loop version of this could be...

n <- nrow(mat)
for( i in 1:n ){
    mat[i,] <- c( tail( mat[i,] , i-1 ) , head( mat[i,] , n-(i-1)  ) )
}