Although it might visually be joining characters, that is not necessarily what you need. The code below should be one of the faster methods, although it breaks when your elements are larger than 9 or non-integer. The nice thing about this system is that you can replace fun with any function (or handle to a function) so you can make sure it does the conversion in a way you want.
bigData=[1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8; ...
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8; ...
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8];
a=mat2cell(bigData, ones(size(bigData,1),1), [8 8]);
fun=@(x) polyval(x,10);
b=cellfun(fun,a);
If you do want to convert to characters, do the join and convert back to double:
fun=@(x) str2double(cell2mat(cellfun(@num2str,num2cell(x),'uni',0)));
Although that function will also break for non-integer values.
