MATLAB: Indexing between two lists

indexindexingMATLAB

Hello. I am fairly new to Matlab and looking for some help with the logic of indexing between two lists.
Matrix A has known distances between points.
A = 
% From      To      DistHzPub

     1       2            100
     1       3            400
     1       4           1000
     2       3            300
     2       4            900
     3       4            600
Matrix B has multiple measurements between the same points.
B = 
% From      To       DistHorz
     1       2         100.01
     1       2         100.04
     1       3         400.02
     1       3         400.05
     1       4        1000.03
     1       4        1000.01
     2       3         300.00
     2       3         300.04
     2       4         900.06
     2       4         900.02
     3       4         600.03
     3       4         600.04
My goal is to match the known distances with the measurements, like this.
C = 
% From      To      DistHzPub
     1       2            100
     1       2            100
     1       3            400
     1       3            400
     1       4           1000
     1       4           1000
     2       3            300
     2       3            300
     2       4            900
     2       4            900
     3       4            600
     3       4            600
Creating an index by hand will get me there…
     idx = [1 1 2 2 3 3 4 4 5 5 6 6]'
     C = A(idx,:)
… but I'm having a hard time figuring out how to generate the index dynamically. Matrix A and B are subject to change in values, size, and order. Thank you.

Best Answer

It seems that you can just use round() on the 3rd column, but since that solution is so obvious, there might be some other reason that you want another solution.
[~, idx] = ismember(B(:,1:2), A(:,1:2), 'rows');
C = A(idx, :);
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