# Why is unique() giving me the matrix after eliminating the common rows for these two matrices?

3 views (last 30 days)
Devika Waghela on 8 Mar 2021
Answered: Steven Lord on 8 Mar 2021
I have A =
0.0000 0.0000
0.0000 1.0000
0.0000 0.0000
0.0000 1.0000
1.0000 0.0000
1.0000 0.0000
1.0000 1.0000
B =
0.1000 0.1000
0.1000 0.9000
0.1000 0.1000
0.1000 0.9000
0.9000 0.1000
0.9000 0.1000
0.9000 0.9000
After using unique I am still getting the exact same matrix as my output. Can anyone tell me why is that?
Jan on 8 Mar 2021
Edited: Jan on 8 Mar 2021
Please post your code and the input data. Currently all we see is A and B and that you mention, that unqiue has been used anywhere.

Jan on 8 Mar 2021
Edited: Steven Lord on 8 Mar 2021
If you use a matrix as input to unique, a vector is replied. So if you matrix is not changed, it cannot be an output of unique(). Because you did not post your code, I guess something like this happens:
B = [0.1000 0.1000
0.1000 0.9000
0.1000 0.1000
0.1000 0.9000
0.9000 0.1000
0.9000 0.1000
0.9000 0.9000];
unique(B); % This is no effect!
% You need:
uB = unique(B)
% Or maybe:
uB = unique(B, 'rows')
[SL: fixed typo]

Steven Lord on 8 Mar 2021
If you're trying to find unique rows, two rows that display the same may not contain the same stored values.
A = [1 2; 1+eps 2] % First and second rows are NOT the same
A = 2×2
1.0000 2.0000 1.0000 2.0000
unique(A, 'rows')
ans = 2×2
1.0000 2.0000 1.0000 2.0000
To allow "close enough" to count you'd want to use uniquetol.
uniquetol(A, eps, 'ByRows', true)
ans = 1×2
1 2