Question

What’s the proper way of checking if the first occurrence any element from a vector exists in a matrix? For example if I have

A = [1, 3] 

and

B = [ 1, 2 ; 
      1, 4 ; 
      2, 3 ; 
      2, 4 ; 
      3, 4 ];

I should get something that returns the indices of matrix B where this condition is met. So for the example I should get.

indx = [1, 1]

I’m using MATLAB R2012a

Answer 1

In order to search for all elements of vector A in matrix B you may use bsxfun:

tmp = bsxfun( @eq, B(:), A );

This comparison disregards the matrix shape of B and treats it as a stack of elements. In your example B has 10 elements and A has 2, therefore tmp is a binary matrix of size 10x2 with true wherever B equals an elements of A.

To find the first element of B that equals any element of A you simply do

idx = find( any( tmp, 2 ), 1, 'first' );

To convert the linear index idx into a row-col pair into B

[r c] = ind2sub( size(B), idx );

Cheers!