Single stacked bar

May I have an additional question, as this Group By element is not very clear for me.

I have another table, with the elements

A | B | C 
------------
true | false | false
false | true | false
true | true | true

If I add another rowid to it, and try to count the sum of trues in the row, it somehow does not work. For some reason I cannot count only trues in multiple rows, following your suggestion.

I would like to have the results:

A | 2
B | 2
C | 1

Sorry for the stupid question, trying to understand the logic of KNIME.