CODEWITHSUNDEEP
matlabvectormatrixcompareelement
roldy
roldy

Reputation: 95

Check vector elements against matrix elements

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

Upvotes: 2

Views: 203

Answers (3)

Kiran
Kiran

Reputation: 8518

Have to tried using strfind command in Matlab.

You can try something like this :

res = strfind(B(:)',A)

This will give all the occurance of A in B. So, the first occurance would be res(1)

Hope it helps

Upvotes: 2

bla
bla

Reputation: 26069

you can use ismember:

vec=ismember(A,B);

or 

vec=ismember(B,A)

depends what you want exultantly (elements of A are found in B or vice versa). Then you can just

[row col]=find(vec,1, 'first')

to get the index position

Upvotes: 3

Shai
Shai

Reputation: 114786

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!

Upvotes: 1

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