Converting between matrix subscripts and linear indices (like ind2sub/sub2ind in matlab)

Question

Let\'s say you have a matrix

m <- matrix(1:25*2, nrow = 5, ncol=5)

How do you go from matrix subscripts (row index, column index) to a lin

Answer 1

Late answer but there's an actual function for ind2sub in the base package called arrayInd

m <- matrix(1:25, nrow = 5, ncol=5)
# linear indices in R increase row number first, then column
arrayInd(5, dim(m))
arrayInd(6, dim(m))
# so, for any arbitrary row/column
numCol <- 3
numRow <- 4
arrayInd(numRow + ((numCol-1) * nrow(m)), dim(m))
# find the row/column of the maximum element in m
arrayInd(which.max(m), dim(m))
# actually which has an arr.ind parameter for returning array indexes
which(m==which.max(m), arr.ind = T)

For sub2ind, JD Long's answer seems to be the best