Find row and column index of maximum value in a matrix [duplicate]

You could do

## Some data
set.seed(123)
mm <- matrix(rbinom(40, 20, 0.5), 8, 5)
mm
#      [,1] [,2] [,3] [,4] [,5]
# [1,]    9   10    8   11   11
# [2,]   12   10    6   11   12
# [3,]    9   14    9   10    6
# [4,]   13   10   14   11   10
# [5,]   13   11   13    9   12
# [6,]    6   10   11    8    8
# [7,]   10    7   11   14    9
# [8,]   13   13   16   13    8

which(mm == max(mm), arr.ind = TRUE)
#      row col
# [1,]   8   3