search for: argmax_l

Suppose I have A, an n x m matrix, each element is an integer (an index). I also have B, an n x l x m array. I need C, where C[n,m] = B[n, A[n, m], m] I am currently using loops, what would be the "R way" to do this? Another question: let A[n, m] <- argmax_l B[n, l, m] what would be the nicest way of doing this? Currently I am using max.col and a single loop, going though the n's. Background: I solving a discrete-space dynamic programming problem, A is the optimal policy, C is the value function. The structure of the problem allows me to use ma...