How do I sort two arrays relative to each other?

Question

I am trying to make a Student Grade Program where there are 2 arrays: String[] Student and double[] Grade. I cloned them to have a sorted array and an unsorted one.

Arrays:

public class Testcode {
    public static void main(String[] args) {
        String ArrN[] = {"Garcia", "Magsilang", "Magbag"};
        double ArrG[] = {2.5, 1.25, 1.5};

        String ArrN2[] = ArrN.clone();
        double ArrG2[] = ArrG.clone();

        Arrays.sort(ArrN2);
        Arrays.sort(ArrG2);

        System.out.println(Arrays.toString(ArrN1));
        System.out.println(Arrays.toString(ArrN2));
        System.out.println(Arrays.toString(ArrG2));
        System.out.println(Arrays.toString(ArrG2));
    }
}

Now, how do I make an output that looks like the one below (Grade Sorted)

- 1.25               Magsilang
- 1.5                Magbag
- 2.5                Garcia

or (Student Sorted)

- Garcia             2.5
- Magbag             1.5
- Magsilang          1.25

Answer 1

Since you're not dealing individually with only names and grades. I would suggest creating a StudentGrade class for your problem like this:

private static class StudentGrade {
    String name;
    double grade;

    public StudentGrade(String n, double g) {
        this.name = n;
        this.grade = g;
    }
}

You can create an array of StudentGrade[] and sort it with whatever field which fits your use case. I sorted it with name and grade and I was able to see expected output;

StudentGrade[] studentGrades = new StudentGrade[] {
        new StudentGrade("Garcia", 2.5),
        new StudentGrade("Magsilang", 1.25),
        new StudentGrade("Magbag", 1.5)
};

// Sort By Name
System.out.println("(Student Sorted):");
Arrays.sort(studentGrades, Comparator.comparing(o -> o.name));
printStudentGrades(studentGrades);

// Sort by Grade
System.out.println("(Grade Sorted):");
Arrays.sort(studentGrades, Comparator.comparing(o -> o.grade));
printStudentGrades(studentGrades);

This prints this output:

(Student Sorted):
Garcia 2.5
Magbag 1.5
Magsilang 1.25
(Grade Sorted):
Magsilang 1.25
Magbag 1.5
Garcia 2.5

Answer 2

As other said, it makes more sense if you have a separated class StudentGrade , which holds name and grade, and then you take advantage from already implemented algorithm Collections.sort , which from Java 8 accepts method reference of your class.

Here is the code:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class StudentGrade {

    private String name;
    private double grade;

    public StudentGrade(String name, double grade) {
        this.name = name;
        this.grade = grade;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getGrade() {
        return grade;
    }

    public void setGrade(double grade) {
        this.grade = grade;
    }
}

public class Testcode {

    public static void main(String[] args) {

        List<StudentGrade> students = new ArrayList<>();

        students.add(new StudentGrade("Garcia", 2.5));
        students.add(new StudentGrade("Magsilang", 1.5));
        students.add(new StudentGrade("Magbag", 1.25));

        Collections.sort(students, Comparator.comparing(StudentGrade::getGrade));
        System.out.println("Grade Sorted");
        for (StudentGrade studentGrade : students) {
            System.out.println(studentGrade.getGrade() + " " + studentGrade.getName());
        }

        Collections.sort(students, Comparator.comparing(StudentGrade::getName));
        System.out.println("\nStudent Sorted");
        for (StudentGrade studentGrade : students) {
            System.out.println(studentGrade.getName() + " " + studentGrade.getGrade());
        }

    }
}

Output is:

Grade Sorted
1.25 Magbag
1.5 Magsilang
2.5 Garcia

Student Sorted
Garcia 2.5
Magbag 1.25
Magsilang 1.5

Answer 3

I've tried to get your 2nd output. Used Bubble sort to sort the array!

class TestCode {
    public static void main(String[] args) {
        String ArrN[] = {"Garcia", "Magsilang", "Magbag"};
        double ArrG[] = {2.5, 1.25, 1.5};

        //bubble sort based on ArrG array
        for (int i = 0; i < ArrG.length - 1; i++) {
            for (int j = 0; j < ArrG.length - i - 1; j++) {
                if (ArrG[j] < ArrG[j + 1]) {
                    double temp = ArrG[j];
                    ArrG[j] = ArrG[j + 1];
                    ArrG[j + 1] = temp;

                    String tempN = ArrN[j];
                    ArrN[j] = ArrN[j + 1];
                    ArrN[j + 1] = tempN;
                }
            }
        }

        // print the array
        for (int i = 0; i < ArrG.length; i++) {
            System.out.println(ArrN[i] + " " + ArrG[i]);
        }
    }
}

Output:

Garcia 2.5
Magbag 1.5
Magsilang 1.25

This is a basic approach! You can also use a Class or built-in Array() methods!

Answer 4

To get a sorted copy of two arrays with respect to each other you can first link in pairs the elements of these arrays, and then sort these pairs - you get a sorted list. As a container for each pair you can use Map.Entry , or an array, or some class . For example:

String[] arrN = {"Garcia", "Magsilang", "Magbag"};
double[] arrG = {2.5, 1.25, 1.5};

List<Map.Entry<String, Double>> list = IntStream
        // assuming the two arrays are the same length,
        // iterate over the indices of the first array
        .range(0, arrN.length)
        // link a pair of two elements
        .mapToObj(i -> Map.entry(arrN[i], arrG[i]))
        // collect a list of map entries
        .collect(Collectors.toList());

// sort by name
list.sort(Map.Entry.comparingByKey());
list.forEach(System.out::println);
//Garcia=2.5
//Magbag=1.5
//Magsilang=1.25

// sort by grades
list.sort(Map.Entry.comparingByValue());
list.forEach(System.out::println);
//Magsilang=1.25
//Magbag=1.5
//Garcia=2.5

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^{See also: How do I relate one array input to another?}