Can I use UNIQUE to get a count of the number of times each element is repeated?

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I would like to know if the UNIQUE function has the capability of returning the number of times each element appears in an array.

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 14 Apr 2011
The ability to return the count of each unique element is not available in the UNIQUE function in MATLAB.
To work around this issue, use the ARRAYFUN function to test each element of an array, determining the number of times each element is equal to an element of original vector.
For example:
a = [12 34 78 8 12 3 34 34];
c = arrayfun(@(x)length(find(a == x)), unique(a), 'Uniform', false);
cell2mat(c)
  1 Comment
Zenin Easa Panthakkalakath
Edited: Zenin Easa Panthakkalakath on 21 Apr 2022
Ideally, the following histogram based method should work for this purpose and I wanted to use that as it is faster. However, it doesn't work for large data as there is a limit to the maximum number of bins which is or .
c = histcounts(sort(a), 'BinMethod', 'integers');
c(c == 0) = [];
A workaround that I found for the same is to use categorical arrays.
c1 = histcounts(categorical(a));
c1(c1 == 0) = [];

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More Answers (1)

Lola Davidson
Lola Davidson on 6 Sep 2022
As of R2019a, you can use groupcounts for this:
>> a = [12 34 78 8 12 3 34 34]';
>> [counts, groupnames] = groupcounts(a)
counts =
1
1
2
3
1
groupnames =
3
8
12
34
78

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