How to sort two arrays with respect to eachother.

Question

I have 2 arrays:

private String[] placeName;
private Double[] miles;

The data in them look like this:

placeName = {"home", "away", "here"};
miles = {111, 11, 3};

The position of the values match to each other. ie home = 111 and away = 11

I need to sort these arrays together so I don't lose how they are matched by the the number- lowest to highest. What is the best way to accomplish this? Do I need to combine the arrays first?

If the `placeName` is unique, use a `TreeMap` populate `placeName` as `key` and `miles` as `value`. — Sajan Chandran, Jun 02 '14 at 16:34
Can't you have 1 2 dimensional array and sort it on one field? http://stackoverflow.com/questions/4907683/sort-a-two-dimensional-array-based-on-one-column — cp5, Jun 02 '14 at 16:36
@SajanChandran I think he wants to sort by distance, not by placeName. — user949300, Jun 02 '14 at 16:40

indivisible · Accepted Answer · 2014-06-02T17:21:10.610

Since the two values are so tightly coupled together I would actually write a custom class to contain the information and then sort those classes instead of playing around with raw arrays. Doing so would leave you open to many possible bugs down the line.
This allows for much better control, data encapsulation and future expansion of what methods or data your class may contain.

public class MyDistance implements Comparable<MyDistance> {
    private String placename;
    private double mileage;

    public MyDistance(String placename, double milage) {
        this.placename = placename;
        this.milage = milage;
    }

    public String getPlacename() {
        return this.placename;
    }

    public double getMilage() {
        return this.milage;
    }

    @Override
    public int compareTo(MyDistance anotherDistance)
    {
        return milage.compareTo(anotherDistance.getMilage());
    }
}

If you want more flexibility in your sort then instead of having your MyDistance class implement Comparable you can write a custom Comparator<MyDistance> class:

public class DistanceComparator extends Comparator<MyDistance> {
    @Override
    public int compare(MyDistance dist1, MyDistance dist2) {
        return dist1.getMilage().compareTo(dist2.getMilage());
    }
}

You can use this Comparator to sort using Collections:

List<MyDistance> distanceList = getDistanceListSomehow();
Collections.sort(distanceList, new DistanceComparator());

You are not restricted to a List, I just used it for explanatory purposes. You should look at the full range of Java Collections types to best choose one that suits your purposes. As a suggestion though, the ArrayList type is easy to use and retains order like you would want.

Technically, this `MyDistance` class should implement `Comparable`, with changes to the argument to `compareTo()`. — user949300, Jun 02 '14 at 16:44

score 2 · Answer 2 · answered Jun 02 '14 at 16:37

2

One way is to create a TreeMap. Assuming you are sorting by miles.

TreeMap tm = new TreeMap<Double, String>();
for (int i=0; i<miles.length; i++) {
  tm.put(miles[i], placeName[i]);
}

// tm is already sorted - iterate over it...

NOTE: IF you have places with the same exact distance in miles this will not work. e.g. if you had a "work" that was 11 miles, just like "away", this won't work. You'd probably want some form of MultiMap for that...

answered Jun 02 '14 at 16:37

user949300

15,364
7
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why use the miles as the key? that seems to needlessly introduce problems. use the name as the key, and you only get collisions of the same name – Adam Yost Jun 02 '14 at 16:40
Because he wants to sort by miles. – user949300 Jun 02 '14 at 16:41
downvote was removed. I missed the info that he needed it sorted by miles. – Adam Yost Jun 02 '14 at 16:43
+1 for pointing out the potential loss of data from duplicate key/distances. Certainly needed to be mentioned. – indivisible Jun 02 '14 at 17:24
This answer may be the simplest that works but Im worried about the data loss possibility, either way nice solution that could be useful for others +1 – BluGeni Jun 02 '14 at 18:01
Thanks. @indivisible has the thorough answer that always works, (I gave him an upvote) but it is a lot more work. Mine is a shortcut appropriate for many, but not all, situations. – user949300 Jun 02 '14 at 18:29

score 0 · Answer 3 · answered Jun 02 '14 at 16:37

0

Maybe put the arrays in a TreeMap and sort it

SortedMap<Double,String> map = new TreeMap<>();
map.put(111,"home");
map.put(11,"away");
map.put(3,"here");

The elemtns are inserted sorted by their key

answered Jun 02 '14 at 16:37

wastl

2,643
14
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How to sort two arrays with respect to eachother.

3 Answers3