package streams;

import students.Student;

import java.sql.SQLOutput;

import java.util.List;

import java.util.stream.Collectors;

public class UsingCollectors {

public static String letterGrade(Student s) {

double gpa = s.getGpa();

if (gpa > 3.75) return "A";

if (gpa > 3.35) return "B";

if (gpa > 2) return "C";

return "D";

}

public static void main(String[] args) {

List<Student> roster = List.of(

Student.of("Fred", 3.4, "Math", "Physics"),

Student.of("Jim", 2.4, "Journalism"),

Student.of("Jimmy", 2.5, "Journalism"),

Student.of("James", 2.3, "Journalism"),

Student.of("Jimbo", 3.5, "Journalism"),

Student.of("Jimmina", 3.8, "Journalism"),

Student.of("Sheila", 3.9, "Math", "Physics", "Quantum Mechanics", "Astrophysics")

);

var map = roster.stream()

.collect(Collectors.groupingBy(s -> letterGrade(s)));

map.entrySet().stream()

.map(e -> "Students with grade " + e.getKey() + " are " + e.getValue())

.forEach(s -> System.out.println(s));

roster.stream()

.collect(Collectors.groupingBy(s -> letterGrade(s), Collectors.counting()))

.entrySet().stream()

.map(e -> e.getValue() + " students scored grade " + e.getKey())

.forEach(s -> System.out.println(s));

roster.stream()

.collect(Collectors.groupingBy(s -> letterGrade(s),

Collectors.mapping(s -> s.getName(),

Collectors.joining(", "))))

.entrySet().stream()

.map(e -> e.getValue() + " scored grade " + e.getKey())

.forEach(s -> System.out.println(s));

}

}