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Unique elements in cell array

version (1.4 KB) by Patrick Mineault
unique for numeric cell arrays. If c = {[0],[1,2],[0],[8],[1,2]} returns {[0],[1,2],[8]}


Updated 08 Jun 2011

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function [Au, idx, idx2] = uniquecell(A)

Same as built-in unique, but works for cell arrays where each element is a numeric array.

For A a cell array of matrices (or vectors), returns Au, which contains the unique matrices in A, idx, which contains the indices of the last appearance of each such unique matrix, and idx2, which contains th indices such that Au(idx2) == A

Example usage:

A = {[1,2,3],[0],[2,3,4],[2,3,1],[1,2,3],[0]};
[Au,idx,idx2] = uniquecell(A);

Results in:

idx = [6,5,4,3]
Au = {[0],[1,2,3],[2,3,1],[2,3,4]}
idx2 = [2,1,4,3,2,1]

Algorithm: uses cellfun to translate numeric matrices into strings then calls unique on cell array of strings and reconstructs the initial matrices.

Cite As

Patrick Mineault (2020). Unique elements in cell array (, MATLAB Central File Exchange. Retrieved .

Comments and Ratings (14)

Ilya Tyuryukanov

Very useful

Punit Rathore

Katharina Hofer

Would be exactly what I need, but unfortunately it does not take matrix shape into account and thus claims that the two matrices in the example below are identical:
uniquecell([{[1 1 1; 1 1 0]},{[1 1; 1 1; 1 0]}])
which leads to only one of them in the output

I fixed the issue by adding a line at the top and modifying the second line
A_mod = cellfun(@(x) padarray(x,ones(ndims(x),1),'post'),A,'UniformOutput',false); % add this line
B = cellfun(@(x) num2str(x(:)'),A_mod,'UniformOutput',false); % replace the A in the original code for A_mod (only in this line)

There might be more efficient ways to fix this.
Also, I have not tested this extensively, so I do not know whether this might introduce issues in some cases.

Thank you for the function!



Excellent function. Thank you.

Sapna S

Thanks, this function makes my calculation a lot simple

Tobi Busari

This is really helpful!


Great work.

I Chieh Chen

Really nice, thanks a lot~

Kevin Bartlett


Good, but limited usage only to numeric matrixes.

Jessica Lam

Really Useful.
Thanks so much=)

MATLAB Release Compatibility
Created with R2008b
Compatible with any release
Platform Compatibility
Windows macOS Linux

Inspired: uniqueCellGeneralized(A), uniqueCells