How to count repetition of a row in a matrix?

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Mr M.
Mr M. on 13 Nov 2018
Commented: Mr M. on 13 Nov 2018
I have a matrix: M = [1,2; 2,3; 1,5; 2,3; 1,4; 1,6; 2;3, 8,9]; And I want to check number of occurance of a given row, for example [2,3]. How to do that without for cycle?

Accepted Answer

Stephen23
Stephen23 on 13 Nov 2018
Edited: Stephen23 on 13 Nov 2018
>> M = [1,2; 2,3; 1,5; 2,3; 1,4; 1,6; 2,3; 8,9];
>> R = [2,3];
Method one: eq: and all:
>> nnz(all(M==R,2))
ans = 3
For MATLAB versions before R2016b use bsxfun and eq:
>> nnz(all(bsxfun(@eq,M,R),2))
ans = 3
Method two: ismember:
>> nnz(ismember(M,R,'rows'))
ans = 3
  1 Comment
Mr M.
Mr M. on 13 Nov 2018
sum(ismember(M,R,'rows')) is the same?

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