Get all diagonal vectors from matrix

Question

I\'m trying to figure out how to get all the diagonals of a matrix. For example, say I have the following matrix: A <- matrix(1:16,4)

using the diag(A)

Answer 1

Since you're dealing with square matrices, it should be really easy to convert Gavin's answer into a small function that first calculates the range that should be used as the offset values. Here's such a function:

AllDiags <- function(inmat, sorted = TRUE) {
  Range <- ncol(inmat) - 1
  Range <- -Range:Range
  if (isTRUE(sorted)) Range <- Range[order(abs(Range))]
  lapply(Range, function(x) {
    inmat[row(inmat) == (col(inmat) - x)]
  })
}

Here's the output on your sample matrix "A".

AllDiags(A)
# [[1]]
# [1]  1  6 11 16
# 
# [[2]]
# [1]  2  7 12
# 
# [[3]]
# [1]  5 10 15
# 
# [[4]]
# [1] 3 8
# 
# [[5]]
# [1]  9 14
# 
# [[6]]
# [1] 4
# 
# [[7]]
# [1] 13