## How to convert Arraylist into 2D double[][] array

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I have an `ArrayList` which has objects of `Coord`s which are x and y:

```ArrayList<Coords> positionsArrayList = new ArrayList<>(values);
```

```class Coords {
int x;
int y;

public boolean equals(Object o) {
Coords c = (Coords) o;
return c.x == x && c.y == y;
}

public Coords(int x, int y) {
super();
this.x = x;
this.y = y;
}

public int hashCode() {
return new Integer(x + "0" + y);
}
}
```

Now i want to extract this x and y in form of 2D array `double[][]`. Just like

`double[][] vector={{0,0},{1,1},{2,2}}`

I have tried this code:

```for (Coords value : positionsArrayList) {
positions = new double[][]{{value.x, value.y}};
}
```

What you can do is use traditional for loop to achieve the result:

```positions = new double[positionsArrayList.size()][2];
for(int i =0; i < positionsArrayList.size(); i++){
positions[i][0] = positionsArrayList.get(i).getX();
positions[i][1] = positionsArrayList.get(i).getY();
}
```

How to convert a list of list integers to 2D int array in Java, how to print 2d arraylist in java 2d dynamic arraylist java convert list to 2d I'm trying to convert an ArrayList of Doubles[] to a normal double 2D array. My code: Solutions 1. If you want a true 2D ArrayList of Doubles then the type of ec should be ArrayList<ArrayList<Double>>.But because we can't use toArray(), we manually loop instead.

The statement:

```positions = new double[][]{{value.x, value.y}};
```

reassigns the reference each time. Finally, `positions` will "point to" (contain) the last tuple, that's why you see it as the result.

Converting 2D ArrayList to 2D Array, Two-dimensional arrays were introduced in Subsection 3.8.5, but we haven't done Each row, in turn, is a list of values separated by commas and enclosed A neat solution is to use an ArrayList instead of an array to hold the moves as we� Doubles.asList(new double[]{1d,2d}); Doubles.asList(1d,2d); Also, the Guava version doesn't do a full traverse, it's a live List view of the primitive array, converting primitives to Objects only when they are accessed.

You could assign each coordinates value for each index like:

```double[][] positions = new double[positionsArrayList.size()][2];

for (int i = 0; i < positionsArrayList.size(); i++) {
positions[i][0] = positionsArrayList.get(i).x;
positions[i][1] = positionsArrayList.get(i).y;
}
```

Or if you're familiar with stream:

```double[][] positions= positionsArrayList.stream()
.map(coords -> new double[]{coords.x, coords.y})
.toArray(double[][]::new);
```

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