Assuming that the non-diagonal values are exactly zero, then you could use varfun something like this:
>> T = cell2table({'A',1,0,0;'A',0,2,0;'A',0,0,3;'B',4,0,0;'B',0,5,0;'B',0,0,6})
T =
Var1 Var2 Var3 Var4
____ ____ ____ ____
'A' 1 0 0
'A' 0 2 0
'A' 0 0 3
'B' 4 0 0
'B' 0 5 0
'B' 0 0 6
>> U = varfun(@sum,T,'GroupingVariables','Var1')
U =
Var1 GroupCount sum_Var2 sum_Var3 sum_Var4
____ __________ ________ ________ ________
A 'A' 3 1 2 3
B 'B' 3 4 5 6
Of course you can rename/remove those table variables as required.
