sort_employee_average_salary/2

Exerciții › Model parțial, Exercițiul 3

Model parțial, Exercițiul 3 advanced Predicate predefinite pe liste Recursivitate pe liste

Primind o listă identică celei de la Exercițiul 2, în lista de rezultat ordonați angajații după salariul mediu câștigat, în ordine descrescătoare.

?- sort_employee_average_salary([employee_salary(peter, 1000), employee_salary(oliver, 1200),
                                  employee_salary(sam, 700), employee_salary(oliver, 800),
                                  employee_salary(sam, 900), employee_salary(sandra, 4500),
                                  employee_salary(peter, 1200), employee_salary(oliver, 400)], Result).
Result = [(sandra, 4500), (peter, 1100), (oliver, 800), (sam, 800)]

Hint: folosește predsort/3 cu un comparator custom care compară salariile în ordine inversă. Vezi Predicate predefinite pe liste.

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% Presupunem definite sum_and_count_by_name/4, remove_by_name/3, employee_average_salary/2
sum_and_count_by_name(_, [], 0, 0) :- !.
sum_and_count_by_name(Name, [employee_salary(Name, CurrentSalary) | Tail], Sum, Count) :-
    sum_and_count_by_name(Name, Tail, SumTail, CountTail),
    Sum is SumTail + CurrentSalary,
    Count is CountTail + 1, !.
sum_and_count_by_name(Name, [_ | Tail], Sum, Count) :-
    sum_and_count_by_name(Name, Tail, Sum, Count).

remove_by_name(_, [], []).
remove_by_name(Name, [employee_salary(Name, _) | Tail], TR) :-
    remove_by_name(Name, Tail, TR), !.
remove_by_name(Name, [H | T], [H | TR]) :-
    remove_by_name(Name, T, TR).

employee_average_salary([], []) :- !.
employee_average_salary([employee_salary(Name, Salary) | Tail], [(Name, Average) | TR]) :-
    sum_and_count_by_name(Name, [employee_salary(Name, Salary) | Tail], Sum, Count),
    Average is Sum / Count,
    remove_by_name(Name, [employee_salary(Name, Salary) | Tail], NewList),
    employee_average_salary(NewList, TR).

% my_cmp(Order, Pair1, Pair2) :- ...
% sort_employee_average_salary(InputList, SortedList) :- ...

sum_and_count_by_name(_, [], 0, 0) :- !.
sum_and_count_by_name(Name, [employee_salary(Name, CurrentSalary) | Tail], Sum, Count) :-
    sum_and_count_by_name(Name, Tail, SumTail, CountTail),
    Sum is SumTail + CurrentSalary,
    Count is CountTail + 1, !.
sum_and_count_by_name(Name, [_ | Tail], Sum, Count) :-
    sum_and_count_by_name(Name, Tail, Sum, Count).

remove_by_name(_, [], []).
remove_by_name(Name, [employee_salary(Name, _) | Tail], TR) :-
    remove_by_name(Name, Tail, TR), !.
remove_by_name(Name, [H | T], [H | TR]) :-
    remove_by_name(Name, T, TR).

employee_average_salary([], []) :- !.
employee_average_salary([employee_salary(Name, Salary) | Tail], [(Name, Average) | TR]) :-
    sum_and_count_by_name(Name, [employee_salary(Name, Salary) | Tail], Sum, Count),
    Average is Sum / Count,
    remove_by_name(Name, [employee_salary(Name, Salary) | Tail], NewList),
    employee_average_salary(NewList, TR).

% comparator descrescător — inversăm argumentele compare
my_cmp(X, (_, Salary1), (_, Salary2)) :-
    compare(X, Salary2, Salary1).

sort_employee_average_salary(InputList, SortedList) :-
    employee_average_salary(InputList, TempList),
    predsort(my_cmp, TempList, SortedList).

Tastează o interogare (ex. father_of(sandra, X).) și apasă Enter — sau apasă pe un caz de test de mai jos.

Cazuri de test (1 — apasă pe unul ca să îl rulezi, sau Verifică pentru toate)

sort_employee_average_salary([employee_salary(peter,1000), employee_salary(oliver,1200), employee_salary(sam,700), employee_salary(oliver,800), employee_salary(sam,900), employee_salary(sandra,4500), employee_salary(peter,1200), employee_salary(oliver,400)], R).

așteptat: R = [(sandra,4500.0),(peter,1100.0),(oliver,800.0),(sam,800.0)]