finding matching rows in matrix

Question

Suppose I have an (m x n) matrix Q, and a row vector r, e.g.

Q = [ 1 2 3 ; 4 2 3 ; 5 6 7 ; 1 2 3 ; 1 2 3 ; 1 2 5 ];

r = [ 1 2 3 ];

What is the easiest way to obtain a logical vector (of length m) that indicates which of the rows in Q are identical (for all elements) to the specified row r?

In the sample case above, that should be

[ 1 0 0 1 1 0 ];

Answer 1

You can use ismember and do it in a single line:

>> ismember(Q,r,'rows')'

ans =

     1     0     0     1     1     0

Answer 2

all(bsxfun(@eq, r, Q),2)'

bsxfun(@eq, r, Q) compares each row and returns a matrix with same size as Q:

>> bsxfun(@eq, r, Q)

ans =

   1     1     1
   0     1     1
   0     0     0
   1     1     1
   1     1     1
   1     1     0

the all function computes if the result of bsxfun is all true along each row separately. Thus it returns:

>> all(ans,2)'

ans =

   1     0     0     1     1     0

and yeah, there is also a transpose operator ' to match your desired row output