Question

I have an n-by-m rectangular matrix (n != m). What’s the best way to find out if there are any duplicate rows in it in MATLAB? What’s the best way to find the indices of the duplicates?

Answer 1

Use unique() to find the distinct row values. If you end up with fewer rows, there are duplicates. It’ll also give you indexes of one location of each of the distinct values. All the other row indexes are your duplicates.

x = [
    1 1
    2 2
    3 3
    4 4
    2 2
    3 3
    3 3
    ];
[u,I,J] = unique(x, 'rows', 'first')
hasDuplicates = size(u,1) < size(x,1)
ixDupRows = setdiff(1:size(x,1), I)
dupRowValues = x(ixDupRows,:)