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

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

Answer 1

[MathWorks Support Team]

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)

[Zenin Easa Panthakkalakath]

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) = [];

Answer 2

[Lola Davidson]

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