Sort an arraylist of an arraylist of doubles

[clementer]

I am looking to sort an arraylist of arraylist of doubles and I require help?

I was informed that I need to implement comparator or comparable and then use the collection.sort to sort the list of list in order...

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

If you look at the list of list as the following example:

c1-5.0,4.5,10.3,3.5

c2-2.5,1.0,7.8,8.6

c3-6.0,5.6,9.6,9.5

It show go to this

c1-2.5,1.0,7.8,3.5

c2-5.0,4.5,7.8,8.6

c3-6.0,5.6,10.3,9.5

[JamesCherrill]

An ArraylIst of ArrayLists is like a 2d array. Which means that there's no single definition of what it means to sort it. Eg
Sort each sub list ?
sort the sublists within the main list according to some criteria ?
sort all of the data and store the result in the same sized 2d array?
(etc).

You need to specify what you mean by sort in this case.

ps: the Double class already implememnts Comparable, so you can use Collections.sort on a List of Doubles without any other code.

[tinstaafl]

Here's a way that is in place, that uses bubble sort.

  public static void sortColumns(ArrayList<ArrayList<Double>> arr){
      int limit = arr.size();
      boolean isSwapped = false;
      for(int col = 0; col < limit; ++col){
          do{
            isSwapped = false;            
            for(int row = 0; row < limit - 1; ++row){
                if(arr.get(row).get(col) > arr.get(row+1).get(col)){
                    swap(arr,row,col,row+1,col);
                    isSwapped = true;
                }
            }
          }while(isSwapped);

      }      
  }
  private static void swap(ArrayList<ArrayList<Double>> arr, int rowA, int colA, int rowB, int colB){
      Double temp = arr.get(rowA).get(colA);
      arr.get(rowA).set(colA,arr.get(rowB).get(colB));
      arr.get(rowB).set(colB, temp);
  }

[JamesCherrill]

Why write your own bubble sort when Collections.sort exists and does it better?

[tinstaafl]

How would you write a function for Collection.sort to do that? It doesn't normally sort by columns.