MATLAB: Summing the elements of cell arrays for only certain values

cell arrays

Does anyone know an efficient way to sum up the last value in a unique instances of a cell array of strings?
For instance 
           A = {'a', 'b', 'c', 2 
                'a', 'b', 'd', 3 
                'b', 'c', 'd', 7 
                'a', 'b', 'd', 10};
the answer that I would return would be every unique combination so I would return a cell array with three unique strings, with values of 2, 7, and 13.

Best Answer

[~,~,j] = unique(A(:,1:3)) ;
[~,x,k] = unique(reshape(j,[],3),'rows')
S = accumarray(k,[A{:,4}])
out = [A(x,1:3) num2cell(S)]
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