azaz

GroupByDemoInJava8.kt

package fr.francetv.francetvsport.arch.presentation.main.navigations

import java.io.IOException
import java.util.*
import java.util.stream.Collectors


object GroupByDemoInJava8 {
    @Throws(IOException::class)
    @JvmStatic
    fun main(args: Array<String>) {
        val people: MutableList<Person> = ArrayList()
        people.add(Person("John", "London", 21))
        people.add(Person("Swann", "London", 21))
        people.add(Person("Kevin", "London", 23))
        people.add(Person("Monobo", "Tokyo", 23))
        people.add(Person("Sam", "Paris", 23))
        people.add(Person("Nadal", "Paris", 31))
        // Now let's group all person by city in pre Java 8 world
        val personsByCity: MutableMap<String, MutableList<Person>?> = HashMap()
        for (p in people) {
            if (!personsByCity.containsKey(p.city)) {
                personsByCity[p.city] = ArrayList()
            }
            personsByCity[p.city]!!.add(p)
        }
        println("Persons grouped by cities : $personsByCity")
        //   //   Java 8 way to group object by a property key
        val personsByCity2 = people.stream().collect(Collectors.groupingBy { p: Person -> p.city })
        val personByAge = people.stream().collect(Collectors.groupingBy { p: Person -> p.age })
        //   System.out.println("Person grouped by age in Java 8: " + personByAge);

        people.groupBy { it.city }.also { println("KT with groupBy $it") }
        people.groupingBy { it.city }.sourceIterator().forEach {
            println("KT with groupingBy $it")
        }
        people.groupingBy { it.city }.fold(mutableMapOf<String, MutableList<Person>>()) { map, person ->
            val persons = map[person.city] ?: mutableListOf()
            persons.add(person)
            map.putIfAbsent(person.city, persons)
            map
        }.also {
            println("MP with effff $it")
        }
    }
}

private data class Person(var name: String, var city: String, var age: Int) {
    override fun toString(): String {
        return String.format("%s(%s,%d)", name, city, age)
    }
}