How to vectorize this operation on every row of a matrix

Question

I have a matrix filled with TRUE/FALSE values and I am trying to find the index position of the first TRUE value on each row (or retur

Answer 1

Not sure this is any better, but this is one solution:

> x2 <- t(t(matrix(as.numeric(x), nrow=10)) * 1:3)
> x2[x2 == 0] <- Inf
> rowMins(x2)
 [1] 2 1 1 2 1 1 2 1 1 2

Edit: Here's a better solution using base R:

> x2 <- (x2 <- which(x, arr=TRUE))[order(x2[,1]),]
> x2[as.logical(c(1,diff(x2[,1]) != 0)),2]
 [1] 2 1 1 2 1 1 2 1 1 2