Looping each row from one matrix to the other matrix

Hi.

I have two matrix with unique rows. Matrix A (228 x 9) and B(256 x 9) in one way or another have exact matching rows. I want to find the index where each row of B is a match of any row in A and store a new variable C (where all the indices are found). I tried matching manually per row of B against A. But it's taking me so long. I tried using for loop but I can't seem to figure out with ismember function.

Here's how I did it with single row from B.

[lia, locb] = ismember(A, B(1,:), 'rows'); % starting off from row 1.

Any help would be appreciated.

Cheers

Answer 1

[Adam Danz]

You were close. Instead of referencing only 1 row of B, reference the entire matrix.

[lia, locb] = ismember(A, B, 'rows'); 

Example

A = reshape(1:20,4,5);
B = A([3,1,4],:);  % B is a version of A with scattered rows and 1 row missing.

%     >> A
%     A =
%          1     5     9    13    17
%          2     6    10    14    18
%          3     7    11    15    19
%          4     8    12    16    20
%     >> B
%     B =
%          3     7    11    15    19
%          1     5     9    13    17
%          4     8    12    16    20

[lia, locb] = ismember(A, B, 'rows')

%     lia =
%       4×1 logical array
%        1
%        0
%        1
%        1
%     locb =
%          2
%          0
%          1
%          3

We can see that row 2 of A is not in B since lia(2)==0 and locb(2)==0.

We can also see that row 1 of A is in row 2 of B since locb(1)==2.

[jay16]

Thanks Adam! I just realized now that it's the same with using intersect function. Appreciate your help.