Example usage for java.util.stream Collectors groupingBy

Introduction

In this page you can find the example usage for java.util.stream Collectors groupingBy.

Prototype

public static <T, K, A, D> Collector<T, ?, Map<K, D>> groupingBy(Function<? super T, ? extends K> classifier,
        Collector<? super T, A, D> downstream)

Source Link

Document

Returns a Collector implementing a cascaded "group by" operation on input elements of type T , grouping elements according to a classification function, and then performing a reduction operation on the values associated with a given key using the specified downstream Collector .

Usage

From source file:Main.java

public static void main(String... args) {
    Map<Type, Long> t = Food.menu.stream().collect(Collectors.groupingBy(Food::getType, Collectors.counting()));

    System.out.println(t);/*from   w  w  w  . j  a v a 2s.  co  m*/

}

From source file:Main.java

public static void main(String... args) {
    Map<Type, Integer> o = Food.menu.stream()
            .collect(Collectors.groupingBy(Food::getType, Collectors.summingInt(Food::getCalories)));

    System.out.println(o);//from   www . j av  a  2  s.c  o  m

}

From source file:Main.java

public static void main(String... args) {
    Map<Type, Food> o = Food.menu.stream().collect(Collectors.groupingBy(Food::getType,
            Collectors.collectingAndThen(
                    Collectors.reducing((Food d1, Food d2) -> d1.getCalories() > d2.getCalories() ? d1 : d2),
                    Optional::get)));

    System.out.println(o);/*from   ww w  .jav  a  2 s.c  o m*/

}

From source file:Main.java

public static void main(String... args) {
    Map<Type, Optional<Food>> o = Food.menu.stream().collect(Collectors.groupingBy(Food::getType,
            Collectors.reducing((Food d1, Food d2) -> d1.getCalories() > d2.getCalories() ? d1 : d2)));

    System.out.println(o);/*  w  w w. j av  a  2s.  c  o m*/

}

From source file:Main.java

public static void main(String... args) {
    Map<Type, Set<CaloricLevel>> o = Food.menu.stream()
            .collect(Collectors.groupingBy(Food::getType, Collectors.mapping(dish -> {
                if (dish.getCalories() <= 400)
                    return CaloricLevel.DIET;
                else if (dish.getCalories() <= 700)
                    return CaloricLevel.NORMAL;
                else
                    return CaloricLevel.FAT;
            }, Collectors.toSet())));

    System.out.println(o);// w  ww  . j  ava2 s.c  om

}

From source file:Main.java

public static void main(String[] args) {
    Map<Employee.Gender, String> namesByGender = Employee.persons().stream().collect(Collectors
            .groupingBy(Employee::getGender, Collectors.mapping(Employee::getName, Collectors.joining(", "))));
    System.out.println(namesByGender);
}

From source file:Main.java

public static void main(String[] args) {
    Map<Employee.Gender, List<String>> namesByGender = Employee.persons().stream().collect(Collectors
            .groupingBy(Employee::getGender, Collectors.mapping(Employee::getName, Collectors.toList())));

    System.out.println(namesByGender);
}

From source file:Main.java

public static void main(String[] args) {
    Map<Employee.Gender, Long> countByGender = Employee.persons().stream()
            .collect(Collectors.groupingBy(Employee::getGender, Collectors.counting()));
    System.out.println(countByGender);
}

From source file:Main.java

public static void main(String[] args) {
    Map personsByGenderAndDobMonth = Employee.persons().stream().collect(
            Collectors.groupingBy(Employee::getGender, Collectors.groupingBy(p -> p.getDob().getMonth(),
                    Collectors.mapping(Employee::getName, Collectors.joining(", ")))));

    System.out.println(personsByGenderAndDobMonth);
}

From source file:Main.java

public static void main(String[] args) {
    Map<Gender, Map<Object, String>> personsByGenderAndDobMonth = Employee.persons().stream().collect(
            Collectors.groupingBy(Employee::getGender, Collectors.groupingBy(p -> p.getDob().getMonth(),
                    Collectors.mapping(Employee::getName, Collectors.joining(", ")))));

    System.out.println(personsByGenderAndDobMonth);
}