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matlabmatrixmatrix-indexing

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

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)?

Solution

  • I solved it using the sub2ind function:

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