WISH: rowWhichMin(x) (and also with cols)

[arubio2]

A function that returns the index of the minimum value equivalent to apply(A,1,which.min)

[HenrikBengtsson]

If implemented, the functions should be:

colWhichMins(x)
rowWhichMins(x)

and likely also:

colWhichMaxs(x)
rowWhichMaxs(x)

while at it.

[JoshOBrien]

For the time being, when I needed rowWhichMaxs() functionality, I did this (piggy-backing on rowRanks()), which speeds up things about 10-fold relative to an apply()-based solution:

as.vector((rowRanks(x) == ncol(x)) %*% seq_len(ncol(x)))

[mayer79]

Just a comment: In R base, the function max.col seems to be very efficient already. It does a "rowWhichMaxs"

[wds15]

I also needed this function and ended up with a

((which(t(x==1)) - 1) %% ncol(x)) + 1

version of this. The trick is essentially to cast x to a vector and then fix the indices to be by row. In this case I do know that only one element is 1 in each row! This is also 10x faster than the respective apply approach.