Sorting ArrayList of ArrayList of double and string by the double in Java

Question

I have an arraylist of arraylist which contains a string and an integer. It looks like:

ArrayList<ArrayList> l= {{1.02,"string1"},{0.33,"string2"},{1.15,"string3"},}; 

and I want to sort it by the order of the double number to look like this:

ArrayList<ArrayList> l= {{0.33,"string2"},{1.02,"string1"},{1.15,"string3"},};

I wrote this code but it doesn't work for me and I don't know where is the problem:

public void listSorting(ArrayList<ArrayList> l){
    int min=0;
    for(int i=0;i<l.size();i++){
        min=i;
        for(int j=i+1;j<l.size();j++){
            if((double)(l.get(i).get(0)) < (double)(l.get(min).get(0))){
                min=j;
            }
        }
        ArrayList temp=new ArrayList<>();
        temp.add(l.get(i));
        l.get(i).add(l.get(min));
        l.get(min).add(temp);
    }
}

Answer 1

You made three mistakes:

• Index of double in your list is zero, not one,
• The inner loop needs to compare min item with item at index j , not i ,
• When you swap two elements of type ArrayList , do not create a new array list.

Here is how you can fix your code:

for(int i=0;i<l.size();i++){
    min=i;
    for(int j=i+1;j<l.size();j++){
        if((double)(l.get(j).get(0)) < (double)(l.get(min).get(0))){
            min=j;
        }
    }
    ArrayList temp=l.get(i);
    l.set(i, l.get(min));
    l.set(min, temp);       
}

Demo.