How to sort a multidimensional array of Objects based on a specific element in Java

Question

I'm building a multidimensional array of Objects, and I would want to sort it by a specific element inside the sub-arrays.

I tried Collections.sort and a bubbleSort but they didn't work.

Object[][] fields = {{
      "sam", "mccarty",
      "m", "1988/06/01", 5.0, true
   },
   {
      "tom", "huges",
      "m", "1988/06/01", 7.0, true
   },
   {
      "jim", "ross",
      "m", "1988/06/01", 6.5, true
   }
};

I expect the array sorted by sub-element [4], so:

 {
   {
      "tom", "huges",
      "m", "1988/06/01", 7.0, true
   },
   {
      "jim", "ross",
      "m", "1988/06/01", 6.0, true
   },
   {
      "sam", "mccartney",
      "m", "1988/06/01", 5.5, true
   }
}

Why not create a class containing the elements of a row and have a simple array with objects of that class? — Joakim Danielson, Mar 30 '19 at 19:43
For example 7.0 in { "tom", "huges", "m", "1988/06/01", 7.0, true } — saga, Mar 30 '19 at 19:44
@JoakimDanielson because the code was written by another developer, and I have to proceed by keeping this structure. — saga, Mar 30 '19 at 19:47
Possible duplicate of [How do I use Comparator to define a custom sort order?](https://stackoverflow.com/questions/5245093/how-do-i-use-comparator-to-define-a-custom-sort-order) — MFisherKDX, Mar 30 '19 at 19:48
You have to Use a Comparator Interface for Sorting it by A specific element. — Vishesh Tayal, Mar 30 '19 at 19:46

score 0 · Answer 1 · answered Mar 30 '19 at 19:49

If all your fields follow the same schema, it could be worth it to wrap them around inside some object, say Person, so that you have a one-dimensional array, and then sort said array using a custom comparator.

You could do something like this:

Person[] fields = {
    new Person("sam", "mccarty", "m", "1988/06/01", 5.0, true),
    ...
};
// Assuming you want things to be sorted in descending order like in your example.
Collections.sort((o1, o2) -> o2.getFourth() - o1.getFourth());

You can find more info on comparators in the docs here.

Youcef LAIDANI · Answer 2 · 2019-03-30T20:01:13.300

You can use :

Arrays.sort(fields, (o1, o2) -> Double.compare((Double) o1[4], (Double) o2[4]));

Outputs of double values after sort is :

5.0
6.5
7.0

Better Solution

but I would create an Object, put the necessary field like so :

class MyObject{
    private String fname;
    private String lname;
    private String gender;
    private LocalDate birthDay;
    private Double note;
    private boolean check;
   // @Getter @Setter @Constructors
}

then the sort can be easy :

MyObject[] array = {...};
Arrays.sort(array, Comparator.comparing(MyObject::getNote));

How to sort a multidimensional array of Objects based on a specific element in Java

2 Answers2

Better Solution