Find similar values in a matrix
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I am currently working with large data sets, on the range of 500k-1m rows of data in any given matrix. (nx3)
I want to know how to sift through the rows of the matrix to see if any of the rows have the same values in them.
ex. [1 2 3; 2 3 4; 3 4 5; 4 5 6; 1 2 3; 5 6 7]
I want to remove the second [1 2 3] row, such that [1 2 3; 2 3 4; 3 4 5; 4 5 6; 5 6 7]
Can anyone help me with this?
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Accepted Answer
Star Strider
on 2 Feb 2016
The unique function can help here:
A = [1 2 3; 2 3 4; 3 4 5; 4 5 6; 1 2 3; 5 6 7];
[Au,ia,ic] = unique(A, 'rows', 'stable');
RowIdxFreq = accumarray(ic, 1);
RowIdxFreq =
2
1
1
1
1
The ‘RowIdxFreq’ variable has the frequencies of the occurrences of the rows. Here, row #1 is repeated.
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Star Strider
on 2 Feb 2016
Without having your matrix to experiment with, I can only guess.
See if adding a cell reference (the ‘{}’ brackets) works:
atomPositions = unique(X{:},'rows','stable');
If you have a relatively ‘uncomplicated’ cell array, that should work. If unique still has problems, you might have to use sprintf to convert the numbers to strings before you do the operations in my code. (I assume ‘atom_names’ are already strings.)
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