轉自stackoverflow： Addressing Matlab matrix with Index-matrix

涉及bsxfun的使用。Addressing Matlab matrix with Index-matrix

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.

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))

總結

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