Set a value of a specific column for each row of a matrix

Question

I have a matrix A with m rows and I'd like to set a specific element of each row equal 1. The column index varies from row to row and is specified by a column vector a (with m values). That is, I want A_{i,a_i} = 1. Is there a quick way to do this in Matlab (without a for-loop)?

Answer 1

I solved it using the sub2ind function:

A(sub2ind(size(A), 1:numel(a), a')) = 1