accumarray is for numerics only but if c is going to only be single characters then can probably still use accumarray as chars are treated as numerics for most functions.
>> a=[11;22;22;11;22;11]';
>> b=[10;20;30;10;20;60]';
>> c=['a';'c';'b';'a';'b';'d']';
>> [i, ~,n]=unique(a,'first'); %find unique
>> res = accumarray(n , c ,size(i), @mode)
res =
2×1 char array
'a'
'b'
If you want to do grouping for more general text can look at groupsummary or findgroups / splitapply workflow to use with char vectors or strings.
>> t = table(a,b,c);
>> groupsummary(t,'a','mode',{'b' 'c'})
ans =
2×4 table
a GroupCount mode_b mode_c
__ __________ ______ ______
11 3 10 a
22 3 20 b
