Find similar values in a matrix

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lsutiger1 2016-2-2

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https://ww2.mathworks.cn/matlabcentral/answers/266256-find-similar-values-in-a-matrix

编辑： lsutiger1 2016-2-2

采纳的回答： Star Strider

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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Star Strider 2016-2-2

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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 2016-2-2

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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.)

lsutiger1 2016-2-2

编辑：lsutiger1 2016-2-2

The matrix is a 2520x3 matrix, and yes, atom_names is a 2520x1 vector of strings. I tried converting it to strings using num2str, which did not work, because then I got a "dimension mismatch" error when num2str converted my matrix into a 2520x33 char. Will try to use sprintf.

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