Convert a 2d double array to 2d double arraylist

Question

I have a 2D Double array that is expanding and I am not sure of its final size therefore I want to convert it to a 2d arraylist but not sure how to do this I tried to define the array list first and use addAll(Array) method but it doesn't work. Any suggestion?

I just wrote this code I think it will work fine but I am looking for more efficient way

public class trial {    

 public static void main(String[] arg){

    double[][] Solutions_to_arrange={{1,5,2,8,4,70,50,80},{3,7,4,2,6,60,30,70},{8,1,6,4,2,10,40,60}};
    ArrayList<ArrayList<Double>> Solutions_to_arrange_A=new ArrayList<ArrayList<Double>>();
    for(int i=0;i<Solutions_to_arrange.length;i++){
        Solutions_to_arrange_A.add(new ArrayList<Double>());
        for(int j=0;j<Solutions_to_arrange[0].length;j++){
            Solutions_to_arrange_A.get(i).add(Solutions_to_arrange[i][j]);
        }
    }

    }
}

Also I have question on putting the statement

Solutions_to_arrange_A.add(new ArrayList<Double>());

Should I put it within the loop or its sufficient to call it just once outside the loop

Is it expanding in both dimensions? Do you want an ArrayList<ArrayList<Double>>, or an ArrayList<Double[]>, or something else? — ajb
– ajb, Commented Feb 15, 2015 at 1:35
Your code with a double loop works (I tried it). Unfortunately, since you've defined your array as double[][] and not Double[][], there's really no way to do any better, that I know of. If you make it Double[][], you'll have to put a .0 after every integer, since Java doesn't like converting an unboxed int to a boxed Double automatically. But if you do both of these, you can write code with a single loop using arrays.asList. But this only works in one dimension, so you'd still need one loop. — ajb
– ajb, Commented Feb 15, 2015 at 1:50

Gilson · Accepted Answer · 2017-03-19 22:47:22Z

4

try it:

    Double[][] matriz = {{1d,5d,2d,8d,4d,70d,50d,80d},{3d,7d,4d,2d,6d,60d,30d,70d},{8d,1d,6d,4d,2d,10d,40d,60d}};

    List<List> result = new ArrayList<>();
    for(Double[] array : matriz){
        result.add( Arrays.asList(array) );
    }

If we use primitive types in "Arrays.asList" we will get a list with one primitive array as its unique item. With object type it will works fine.

edited Mar 19, 2017 at 22:47

answered Feb 27, 2015 at 2:11

Gilson

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