JAVA ( 스트림의 그룹화,분할 )

 

--partitioningBy ()   :  스트림을 2분할 한다.

 

 

import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class Student{
	String name;     
	boolean isMale;   //성별
	int hak;          //학년
	int ban;          //반
	int score;
	
	Student(String name, boolean isMale , int hak, int ban, int score){
		this.name =name;
		this.isMale = isMale;
		this.hak = hak;
		this.ban = ban;
		this.score = score;
	}
	String getName() { return name; }
	boolean isMale() { return isMale;	}
	int     getHak() { return hak;  }
	int     getBan() { return ban;  }
	int   getScore() { return score; }
	
	@Override
	public String toString() {
		return String.format("[%s , %s, %d학년 %d반, %d점]",
				name , isMale ? "남" : "여" , hak , ban , score);			
	}
	// groupingBy() 에서 사용 ,, 성적 상 중 하
	enum Level { HIGH , MID , LOW }
}

public class Example7 {

	public static void main(String[] args) {

		Student[] stuArr = {
				new Student("김첫째",true, 1, 1, 300),
				new Student("김둘째",false, 1, 1, 250),
				new Student("김셋째",true, 1, 1, 200),
				new Student("김넷째",false, 1, 2, 150),
				new Student("김다섯",true, 1, 2, 100),
				new Student("김여섯",false, 1, 2, 50),
				new Student("김일곱",false, 1, 3, 100),
				new Student("김여덟",false, 1, 3, 150),
				new Student("김아홉",true, 1, 3, 200),
				
				new Student("김첫째",true, 2, 1, 300),
				new Student("김둘째",false, 2, 1, 250),
				new Student("김셋째",true, 2, 1, 200),
				new Student("김넷째",false, 2, 2, 150),
				new Student("김다섯",true, 2, 2, 100),
				new Student("김여섯",false, 2, 2, 50),
				new Student("김일곱",false, 2, 1, 100),
				new Student("김여덟",false, 2, 1, 150),
				new Student("김아홉",true, 2, 1, 200)
		};
		System.out.print("1. 단순분할 ( 성별로 분할 )");
		System.out.println();
		Map<Boolean, List<Student>> stuBySex = Stream.of(stuArr)
				.collect(Collectors.partitioningBy(Student::isMale));
		
		List<Student> maleStudent = stuBySex.get(true);
		List<Student> femaleStudent = stuBySex.get(false);
		
		for (Student s : maleStudent)  System.out.println(s);
		for (Student s : femaleStudent)  System.out.println(s);
		
		System.out.println();
		System.out.println("2. 단순분할+통계 ( 성별 학생수");
		Map<Boolean, Long> stuNumBySex = Stream.of(stuArr)
			.collect(Collectors.partitioningBy(Student::isMale, Collectors.counting()));
		
		System.out.println("남학생수 : "+stuNumBySex.get(true));
		System.out.println("여학생수 : "+stuNumBySex.get(false));
		
		System.out.println("3. 다중분할(성별 불합격자,100점이하)");
		
		Map<Boolean,Map<Boolean,List<Student>>> failedStuBySex =
				Stream.of(stuArr).collect(Collectors.partitioningBy(Student::isMale,
						Collectors.partitioningBy( s -> s.getScore() <= 100 )));
		
		List<Student> failedMaleStu = failedStuBySex.get(true).get(true);
		List<Student> failedFemaleStu = failedStuBySex.get(false).get(true);
		
		
		for(Student s : failedMaleStu) System.out.println(s);
		for(Student s : failedFemaleStu) System.out.println(s);		
		
	}

}