How to sort 2D array in Java based on two column's value

Question

I have a problem where I should sort out array of arrays and get sorted indexes of the array, I think some example will demonstrate my problem better than just describing by words. So, I present several examples:

1-example:
n=3 
[1, 4] row=0
[2, 5]
[3, 6] row=2
output should be : 0 1 2 (explanation is below)
2-example:
n=5
[8, 9]  row=0
[4, 6]  row=1
[5, 11] row=2
[3, 4]  row=3
[4, 7]  row=4
[2, 6]  row=5
output should be : 3 5 1 4 0 2(explanation is below)

Sorting criteria mainly based on second column's value, first I should print the second column's smallest value's index, in 1-example it is 4 and it's index is 0 . If we encounter same values in second column as in 2-example (1 and 5 rows are same) then we should compare first columns corresponding values and print the smaller one's index first. Another more precise example of the problem:

n=3
[4, 6]  row=0
[1, 6]  row=1
[2, 6]  row=2
output should be : 1 2 0

EDIT: There is always 2 columns and n rows

yes, if you want I can show you my try, but here I described problem partly, the actual problem is slightly different so the code — Humoyun Ahmad
– Humoyun Ahmad, Commented Nov 29, 2015 at 11:18
Every sorting algorithm would work as soon as you provide the right compare function. — jeerbl
– jeerbl, Commented Nov 29, 2015 at 11:28
@Humoyun if you are satisfied with my answer, please up-vote — Vishal Gajera
– Vishal Gajera, Commented Nov 30, 2015 at 10:46

jeerbl · Accepted Answer · 2015-11-29 11:22:40Z

1

Basically, for this question, I think any sorting algorithm would work. You just need to specify your compare function to compare two elements.

For example, if you want to Bubble sort, in your case, with this algorithm (pseudocode taken from Wikipedia):

procedure bubbleSort( A : list of sortable items )
  n = length(A)
  repeat 
    swapped = false
    for i = 1 to n-1 inclusive do
      if A[i-1] > A[i] then /* COMPARE LINE */
        swap( A[i-1], A[i] )
        swapped = true
      end if
    end for
    until not swapped
end procedure

You just need to replace the comparison on the line commented with COMPARE LINE with a compare function that would compare your objects just like you need (based on the second element and, if equal, the first element).

For example, replace this line by if compare( A[i-1], A[i] ) then.

To summarize, every sorting algorithm would work, as long as you provide the right compare function.

answered Nov 29, 2015 at 11:22

jeerbl

7,9675 gold badges28 silver badges39 bronze badges

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

1 Comment

Humoyun Ahmad Over a year ago

it is right, but I should also keep track of index not just values, main problem I am facing is after sorting I lose initial positions of indexes as they are sorted

Vishal Gajera · Accepted Answer · 2015-11-29 12:06:50Z

0

Here is you complete solution try this,

public class TwoDimensitnArraySort {
public static void main(String[] args) {
    int ary[][] = {{8, 9},{4, 6},{5, 11},{3, 4},{4, 7},{2, 6}};

    ArrayList<TwoDArray> list = new ArrayList<TwoDArray>();

    for(int i = 0;i<ary.length;i++){
        int k = ary[i][0];
        int v = ary[i][1];
        list.add(new TwoDArray(k, v));
    }

    Collections.sort(list);
    int index = 0;
    for(TwoDArray element : list){
        for(int i = 0;i<ary.length;i++){
            if(element.getKey() == ary[i][0] && element.getValue() == ary[i][1]){
                System.out.print(i + " ");
            }
        }
    }
}
}

class TwoDArray implements Comparable<TwoDArray>{
    int key;
    int value;

    public TwoDArray(int key,int value) {
        this.key = key;
        this.value = value;
    }


    public int getKey() {
        return key;
    }



    public void setKey(int key) {
        this.key = key;
    }



    public int getValue() {
        return value;
    }



    public void setValue(int value) {
        this.value = value;
    }



    public int compareTo(TwoDArray o) {
        if(o.getValue() >= this.getValue()){
            return -1;
        }else if (o.getValue() < this.getValue()){
            return 1;
        }
        if(o.getValue() == this.getValue()){
            if(o.getKey() >= this.getKey()){
                return -1;
            }else if (o.getKey() < this.getKey()){
                return 1;
            }
        }

        return 0;
    };
    @Override
    public String toString() {
        return this.key + ":" + this.value;
    }
}

answered Nov 29, 2015 at 12:06

Vishal Gajera

4,2378 gold badges32 silver badges57 bronze badges

3 Comments

jeerbl Over a year ago

"Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime." You just gave that man a fish.

Vishal Gajera Over a year ago

@JérômeBrunel what you mean ?

jeerbl Over a year ago

You threw the solution at him without giving any explanation.

Collectives™ on Stack Overflow

How to sort 2D array in Java based on two column's value

2 Answers 2

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related