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Asked: 2026-05-26T16:08:27+00:00

I am using the command [A,idx] = sort(A) , which sorts the matrix A

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I am using the command [A,idx] = sort(A), which sorts the matrix A columnwise, which is what I want. The idx matrix shows how each column of A has been sorted. Now if I try and access B(idx) MATLAB assumes I am referencing B in an absolute manner. This is however not what I want, I want the columns of B sorted with the same scheme A was sorted with.

I am therefore looking for a command that will index a matrix columnwise. Of course I can easily do this with a loop, but it seems like a pretty poor solution. I have also come up with this solution, but it’s not very pretty

idx = idx+repmat(0:size(idx,1):size(idx,2)*size(idx,1)-1,size(idx,1),1)

Thanks in advance.

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1 Answer

  1. Editorial Team

    Consider the following:

    A = randi([1 10],[5 4]);
[AA,idx] = sort(A);

    Your solution is not bad, you could improve it a bit by replacing the REPMAT call with BSXFUN:

    idx = bsxfun(@plus, idx, 0:size(idx,1):numel(idx)-1);
isequal(AA,A(idx))

    Another alternative is to convert to linear indices using SUB2IND:

    idx = sub2ind(size(idx), idx, repmat(1:size(idx,2),size(idx,1),1));
isequal(AA,A(idx))
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