How to Sort a 2D Double Array by the First Column in Java?

Sorting 2D Arrays Using Java's Arrays.sort()

Arrays.sort() is a versatile sorting function in Java that can be utilized for various data types, including 2D arrays. In this specific scenario, we aim to sort a 2D double array based on the values in the first column.

To achieve this without implementing a custom sorting algorithm, we can leverage the overloaded version of Arrays#Sort(T[] a, Comparator c). By providing a Comparator as the second argument, we can specify our own sorting criteria.

For the given array:

double[][] myArr = new double[mySize][2];
// Initial array contents

1      5
13     1.55
12     100.6
12.1   .85

We can create a comparator that compares the first elements of each row:

Comparator<double[]> comparator = new Comparator<double[]>() {
    @Override
    public int compare(double[] a, double[] b) {
        return Double.compare(a[0], b[0]);
    }
};

Then, we can sort the array using this comparator:

java.util.Arrays.sort(myArr, comparator);

Result:

1      5
12     100.6
12.1   .85
13     1.55

JAVA-8:

In Java 8 and later, we can simplify the comparator using a lambda expression:

Arrays.sort(myArr, Comparator.comparingDouble(o -> o[0]));

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