CODEWITHSUNDEEP
matlab
reddish
reddish

Reputation: 1410

finding matching rows in matrix

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 ];

Upvotes: 12

Views: 18946

Answers (4)

Gunther Struyf
Gunther Struyf

Reputation: 11168

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

Upvotes: 13

neouyghur
neouyghur

Reputation: 1647

a = [1 1 1; 2 2 2; 3 3 3];
b = a(1:2,;);
[temp locb] = ismember(a,b,'rows');
b(locb(locb~=0),:)

ans =

     1     1     1
     2     2     2

Upvotes: 1

petrichor
petrichor

Reputation: 6569

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

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

ans =

     1     0     0     1     1     0

Upvotes: 21

Castilho
Castilho

Reputation: 3187

Easier way with repmat:

a = [1 2 3; 4 5 6; 7 8 9];
t = [4 5 6];
[x,y] = size(a);
r = all(a==repmat(t,y,1), 2)'

Upvotes: 0

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