Given the following matrix lets assume I want to find the maximum value in column two:
mat <- matrix(c(1:3,7:9,4:6), byrow = T, nc = 3)
mat
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 7 8 9
[3,] 4 5 6
I know max(mat[,2]) will return 8. How can I return the row index, in this case row two?
See ?order. You just need the last index (or first, in decreasing order), so this should do the trick:
order(matrix[,2],decreasing=T)[1]
A different way using dplyr:
mat <- matrix(c(1:3,7:9,4:6), byrow = T, nc = 3)
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 7 8 9
[3,] 4 5 6
mat %>% as_tibble() %>% filter( V2 == max(V2) )
# A tibble: 1 x 3
V1 V2 V3
<int> <int> <int>
1 7 8 9