Matrix antidiagonals

Extract or replace the antidiagonal of a matrix, or construct a antidiagonal matrix.

antidiag(x = as.numeric(c(1)), nrow = NULL, ncol = NULL)

antidiag(x) <- value

Arguments

x	matrix, vector or 1D array, or missing.
nrow	number of rows (optional; when x is not a matrix)
ncol	number of columns (optional; when x is not a matrix)
value	either a single value or a vector of length equal to that of the current antidiagonal. Should be of a mode which can be coerced to that of x.

Examples

# Extracting antidiag
antidiag(diag(3))
#> [1] 0 1 0
# Creating antidiagonal matrix
antidiag(7, 3, 3)
#>      [,1] [,2] [,3]
#> [1,]    0    0    7
#> [2,]    0    7    0
#> [3,]    7    0    0
antidiag(1:5, 3, 3)
#>      [,1] [,2] [,3]
#> [1,]    0    0    1
#> [2,]    0    2    0
#> [3,]    3    0    0
# Assigning antidiagonal
mat <- matrix(0, 3, 3)
antidiag(mat) <- c(3, 4, 5)
mat
#>      [,1] [,2] [,3]
#> [1,]    0    0    3
#> [2,]    0    4    0
#> [3,]    5    0    0