Migster:
Tengo una lista de objetos de la lista Cliente (Customer: int id, isActive bool, int billingCount, ...) y quiero la suma y el promedio de billingCount. Por desgracia, mi código no funcionaba. ¿Cómo tengo que cambiar el código para que funcione?
suma y promedio mirada sould como esto:
verdadera 1234
falsa 1234
Map<Boolean, Integer> sum = customer.stream()
.map(c -> c.getIsActive())
.collect(Collectors.groupingBy(c -> c, Collectors.summingInt(Customer::getBillingCount)));
Map<Boolean, Integer> average = customer.stream()
.map(c -> c.getIsActive())
.collect(Collectors.groupingBy(c -> c, Collectors.averagingInt(Customer::getBillingCount)));
}
Obtuve el siguiente error:
Error:(146, 17) java: no suitable method found for collect(java.util.stream.Collector<Customer,capture#1 of ?,java.util.Map<java.lang.Object,java.lang.Integer>>)
method java.util.stream.Stream.<R>collect(java.util.function.Supplier<R>,java.util.function.BiConsumer<R,? super java.lang.Boolean>,java.util.function.BiConsumer<R,R>) is not applicable
(cannot infer type-variable(s) R
(actual and formal argument lists differ in length))
method java.util.stream.Stream.<R,A>collect(java.util.stream.Collector<? super java.lang.Boolean,A,R>) is not applicable
(inference variable T has incompatible bounds
lower bounds: java.lang.Object,Customer
lower bounds: java.lang.Boolean)
Michael Ziober:
No es necesario para el uso map
. Véase más abajo ejemplo:
List<Customer> customers = Arrays.asList(
new Customer(10, true, 5),
new Customer(11, true, 3),
new Customer(20, false, 12),
new Customer(21, false, 11));
Map<Boolean, Integer> sum = customers
.stream()
.collect(Collectors.groupingBy(Customer::isActive, Collectors.summingInt(Customer::getBillingCount)));
System.out.println(sum);
Map<Boolean, Double> avg = customers
.stream()
.collect(Collectors.groupingBy(Customer::isActive, Collectors.averagingInt(Customer::getBillingCount)));
System.out.println(avg);
imprime el código de seguridad:
{false=23, true=8}
{false=11.5, true=4.0}