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matlabmatrixindices

Find column locations of vector elements inside a matrix

Given a vector such as a = [2 5 9] and a matrix such as

    8  11  5 
b = 2   6  1
    4   9  3

What's the best way to find which column of b contains each element of a? In this example I'd want an output like [1 3 2] because 2 is in the first column, 5 is in the third column, and 9 is in the second column. For my purposes it's safe to assume that a number can only appear in one column.

Solution

  • One approach -

    [colID,~] = find(squeeze(any(bsxfun(@eq,b,permute(a,[1 3 2])),1)))

    Or if you would like to avoid squeeze and any -

    [~,colID,~] = ind2sub([size(b) numel(a)],find(bsxfun(@eq,b(:),a)))