如何通过Prolog计算列表长度

Question

l have a list following

List = [['Dev', 'Jon'], ['Dev', 'Darin'], ['Dev', 'Hans'], 
['Test', 'Richard'], ['Test', 'Mike'], ['Test', 'Jon'], ['Test', 'Hans'], 
['Chef', 'Bozho'], ['Chef', 'Mike'], ['Chef', 'Jon']] .

I want to calculate how many times every person appear and add his time step by step for example, the result is following:

[['Dev', 'Jon', 1], ['Dev', 'Darin',1], ['Dev', 'Hans', 1], 
['Test', 'Richard', 1], ['Test', 'Mike', 1], ['Test', 'Jon', 2], ['Test', 'Hans', 2], 
['Chef', 'Bozho', 1], ['Chef', 'Mike', 2], ['Chef', 'Jon', 3]]

thanks very much :)

Answer 1

The solution could be something like this:

count([], _, Zs, Zs).
count([[X,Y]|T], Ys, Zs, Us) :- select([Y,C], Ys, Ys1), C1 is C+1, append(Zs, [[X,Y,C1]], Zs1), count(T, [[Y,C1]|Ys1], Zs1, Us), !.
count([[X,Y]|T], Ys, Zs, Us) :- append(Zs, [[X,Y,1]], Zs1), count(T, [[Y,1]|Ys], Zs1, Us).


transform(L1, L2) :- count(L1, [], [], L2).

We use Ys list to store counters for all people and Zs list to accumulate every person with corresponding index. Hope it helps.