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
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