how to count unique elements of a cell in matlab?

Question

I want to count unique elements of a cell array in Matlab. How can I do this? Thank you.

c = {'a', 'b', 'c', 'a'};
% count unique elements, return the following struct
unique_count.a = 2
unique_count.b = 1
unique_count.c = 1

Answer 1

To count unique elements, you can combine UNIQUE with ACCUMARRAY

c = {'a', 'b', 'c', 'a'};
[uniqueC,~,idx] = unique(c); %# uniqueC are unique entries in c
                             %# replace the tilde with 'dummy' if pre-R2008a

counts = accumarray(idx(:),1,[],@sum); 

To produce the structure, use NUM2CELL and STRUCT:

countCell = num2cell(counts);
tmp = [uniqueC;countCell']; %'

unique_count = struct(tmp{:}) %# this evaluates to struct('a',2,'b',1,'c') 

unique_count = 
    a: 2
    b: 1
    c: 1

Answer 2

Check out count_unique on the file exchange. It uses accumarray or sort depending upon which is the most appropriate. It will also check for nans/infs.