How to deep copy 2 dimensional array (different row sizes)

Question

This is my first question in a community like this, so my format in question may not be very good sorry for that in the first place.

Now that my problem is I want to deep copy a 2 dimension array in Java. It is pretty easy when doin it in 1 dimension or even 2 dimension array with fixed size of rows and columns. My main problem is I cannot make an initialization for the second array I try to copy such as:

int[][] copyArray = new int[row][column]

Because the row size is not fixed and changes in each row index such as I try to copy this array:

int[][] envoriment = {{1, 1, 1, 1}, {0, 1, 6}, {1}};

So you see, if I say new int[3][4] there will be extra spaces which I don't want. Is there a method to deep copy such kind of 2 dimensional array?

score 10 · Accepted Answer · answered Apr 06 '11 at 08:12

10

I think what you mean is that the column size isn't fixed. Anyway a simple straightforward way would be:

public int[][] copy(int[][] input) {
      int[][] target = new int[input.length][];
      for (int i=0; i <input.length; i++) {
        target[i] = Arrays.copyOf(input[i], input[i].length);
      }
      return target;
}

answered Apr 06 '11 at 08:12

Asaf

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Awesome, this is what I seek in general. Thanks for all of the answers they all helped me :) – Apr 06 '11 at 08:32

score 2 · Answer 2 · answered Apr 06 '11 at 08:07

2

You don't have to initialize both dimensions at the same time:

int[][] test = new int[100][];
test[0] = new int[50];

Does it help ?

answered Apr 06 '11 at 08:07

pgras

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Oh this information will help. I never thought of initializing dimensions in different time – Apr 06 '11 at 08:21

score 1 · Answer 3 · answered Oct 24 '14 at 03:12

1

Java 8 lambdas make this easy:

int[][] copy = Arrays.stream(envoriment).map(x -> x.clone()).toArray(int[][]::new);

You can also write .map(int[]::clone) after JDK-8056051 is fixed, if you think that's clearer.

answered Oct 24 '14 at 03:12

Jeffrey Bosboom

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score -2 · Answer 4 · answered Apr 06 '11 at 08:11

-2

You might need something like this:

public class Example {
  public static void main(String[] args) {

    int[][] envoriment = {{1, 1, 1, 1}, {0, 1, 6}, {1}};

    int[][] copyArray = new int[envoriment.length][];
    System.arraycopy(envoriment, 0, copyArray, 0, envoriment.length);
  }
}

answered Apr 06 '11 at 08:11

Shankar Raju

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The code you are proposing is shallow-copying, isn't it? The arraycopy will copy each value of the environment array into the new one. It is: it will copy the references to the original rows. It's not going to copy the sub-arrays. – helios Apr 06 '11 at 08:16
@rlibby and @Helios, are you guys sure it does shallow copy? I thought is does a deep copy. In that case let me revisit. I might be wrong. Thanks for pointing it out. – Shankar Raju Apr 06 '11 at 08:47
1

it is shallow copy, you are copying references to one dimensional arrays, you can check by adding this after your code: envoriment[2][0] = 5; and check copyArray[2][0] is now also 5 – pgras Apr 06 '11 at 09:13

How to deep copy 2 dimensional array (different row sizes)

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