# Duplicate elements in each row

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Isabella Kirksey on 25 Sep 2022
Edited: dpb on 25 Sep 2022
I have the following code to find duplicate elements in each row of a matrix:
for i=1:length
counts=hist(same(i,1:5),13);
a=ismember(3,counts);
b=ismember(2,counts);
c(i)=a+b;
trip(i)=sum(counts==3);
end
The code works but starts to run into runtime issues with big matrix sizes. Is there a way I can do this without using a for loop?

dpb on 25 Sep 2022
Edited: dpb on 25 Sep 2022
Sure, if am reading the desired output correctly -- NB it appears your c variable is indexed incorrectly; it should be a logical array the size of the input array (or it's missing "the curlies" {} to make it a cell array by row).
I'll use "A" here for brevity for the input array...
c=(A==2)|(A==3); % logical array of locations == 2 or 3, address eadh row as c(i,:)
trip=sum(A==3,2); % number == 3 only by row
I'm guessing doing the comparison twice is going to be as fast (or nearly so) as the route of saving the temporary to build the logical array such as
a=(A==2);
b=(A==3);
c=a|b;
trip=sum(b,2);
but you can test both...