Simil to VLOOKUP (but ismember index 0)

Question

Dave 2014-11-22

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https://ww2.mathworks.cn/matlabcentral/answers/163834-simil-to-vlookup-but-ismember-index-0

回答： Dave 2014-11-24

Hello, I have array A 10x1 and array B 3x2 as below

A=[1; 2; 3; 4; 5; 6; 7; 8; 9; 10];
B=[2 100; 4 500; 7 300];

I need to add to the A matrix the values according to the second column of B.

Output should be

A=[1 NaN; 2 100; 3 NaN; 4 500; 5 NaN; 6 NaN; 7 300; 8 NaN; 9 NaN; 10 NaN];

Cannot use ismember because I will have a 0 index (*)

Is there a way to solve this? Thanks

(*) A perhaps similar question I asked here and now moved it as a new question as asked

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Answer 1

Guillaume 2014-11-22

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https://ww2.mathworks.cn/matlabcentral/answers/163834-simil-to-vlookup-but-ismember-index-0#answer_159873

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A simple way would be to fill the 2nd column of A with NaNs and replace some with logical addressing using ismember:

A=[1; 4; 3; 2; 5; 6; 7; 8; 9; 10]; %changed to make sure it works regardless of ordering
B=[2 100; 7 500; 4 300]; %changed to make sure it works regardless of ordering
A = [A nan(size(A, 1), 1)];
[row, locb] = ismember(A, B(:, 1));
A(row, 2) = B(locb(row), 2)

Another option is to use intersect instead of ismember and just use the indices it returns:

A=[1; 4; 3; 2; 5; 6; 7; 8; 9; 10]; %changed to make sure it works regardless of ordering
B=[2 100; 7 500; 4 300]; %changed to make sure it works regardless of ordering
A = [A nan(size(A, 1), 1)];
[~, ia, ib] = intersect(A, B(:, 1));
A(ia, 2) = B(ib, 2)