Ismember function -- return all indexes, not just lowest?

Question

1 个投票

According to the Matlab documentation,

[Lia,Locb] = ismember(A,B) returns an array, Locb, containing the lowest index in B for each value in A that is a member of B.

Is there a way to return an array (or matrix) containing all indexes in B for each value in A that is a member of B?

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Answer 1

Matt J 2013-6-12

编辑：Matt J 2013-6-12

0 个投票

For numeric A and B, I would probably do something like this

 Lia = ismember(A,B)
 idx=find(Lia);
 map=bsxfun(@eq, A(idx),B(:));

Then map(:,i) will be a logical index into B of all points where B equals A(idx(i))

Captain Karnage 2023-6-27

The step idx=find(Lia) is not necessary, you can use A(Lia) to get the same result and it is a faster, more efficient way to index A in MATLAB.

Also, if B is not a vector, this will not work. You would need more steps to search a 2(or more)-D array.

Answer 2

Jan 2013-6-13

0 个投票

Then the output can have different sizes for the different elements of A and a cell is required. What about a simple loop:

Out = cell(1, numel(A))
for iA = 1:numel(A)
  Out{iA} = find(B == A(iA));
end