Sort Three Arrays by ArrayList Index (Row) on a Single Array

Question

In an ArrayList I have three double[ ] arrays that I wish to sort on the third array. The third array is also unsorted.

public class LevelList extends ArrayList<double[]> {

My comparator compares doubles:

import java.util.Comparator;

public class Linearize {
     static final Comparator<double[]> RATIO_ORDER = 
             new Comparator<double[]>() {
                 @Override
                 public int compare(double[] d1, double[] d2) {
                     //Sort the ratios based on the fraction column 2
                     return Double.compare(d1[2], d2[2]);
                 }
         };
}

I then call:

Collections.sort(levelList, Linearize.RATIO_ORDER);
levelList.println();

However, this only results in a sorting of the order of arrays in ArrayList.

In pseudocode, what I wish to achieve is:

For Each Row of ArrayList at Index i
Sort on Array 3

So that this input:

[1.0][2.0][2.1]
[2.0][5.0][2.2]
[1.0][5.0][1.0]

becomes:

[1.0][5.0][1.0]
[1.0][2.0][2.1]
[2.0][5.0][2.2]

because: 2.2 > 2.1 > 1.0

I have demonstrated this under "becomes:" above. Each array should be presented in a column, sorted on the third. — noumenal
– noumenal, Commented Apr 3, 2015 at 10:06
What I got is actually Col1 Col2 Col3 sorts to Col2 Col3 Col1, I guess depending on each column value. — noumenal
– noumenal, Commented Apr 3, 2015 at 10:08
Why extends ArrayList? Avoid extending classes from the collections framework. — Boris the Spider
– Boris the Spider, Commented Apr 3, 2015 at 10:12

Yantraguru · Accepted Answer · 2015-04-03 10:15:07Z

1

I got the desired output. I tested the following code. Did not understand why levellist has to extend arraylist, hence removed that.

public class TestLevelSorting {
public static void main(String[] args) {

    List<double[]> levelList = new ArrayList<double[]>();

    double[] items1 = {1.0, 2.01, 2.1};
    double[] items2 = {2.0, 5.0, 2.2};
    double[] items3 = {1.0, 5.0, 1.0};

    levelList.add(items1);
    levelList.add(items2);
    levelList.add(items3);

    Collections.sort(levelList, Linearize.RATIO_ORDER);

    for(double[] item : levelList){
        System.out.println(Arrays.toString(item));
    }
}
}

class Linearize {
static final Comparator<double[]> RATIO_ORDER = new Comparator<double[]>() {
    @Override
    public int compare(double[] d1, double[] d2) {
        // Sort the ratios based on the fraction column 2
        return Double.compare(d1[2], d2[2]);
    }
};
}

answered Apr 3, 2015 at 10:15

Yantraguru

3,8944 gold badges20 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

noumenal Over a year ago

This works for the example. However, the actual arrays are much longer than in the example. When inserting the actual arrays, the output looks transposed. I am not sure why. Is there a way to return only the head (i.e. first 5 rows) with a loop?

noumenal Over a year ago

Oops. I initialized the size incorrectly. And from there on it was simply: for(int i = 0; i < 5;i++){ for(int o = 0; o < 3; o++){ System.out.print(levelList.get(o)[i] + ", "); } System.out.println(); }

Collectives™ on Stack Overflow

Sort Three Arrays by ArrayList Index (Row) on a Single Array

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related