How to make a new array from an old array?

Question

float[][] pesIAlcada = {
        { 2.4f, 3.1f, 3.07f, 3.7f, 2.7f, 2.9f, 3.2f, 3f, 3.6f, 3.1f },
        { 19f, 18.7f, 22f, 24f, 17f, 18.5f, 21f, 20f, 18.7f, 22f, 18f },
        { 47f, 48f, 49f, 50f, 51f, 52f, 51.5f, 50.5f, 49.5f, 49.1f, 50f },
        { 101f, 104f, 106f, 107f, 107.5f, 108f, 109f, 110f, 112f, 103f } };
/* 
 * I already created an array. And I want to make a new one but some
 * infomation from the old array. How can I do, plz?
 */
float[][] pesNeixement = new float[ROWS][COLS];
for (int i = 0; i < 2; i++) {
    for (int j = 0; j < pesIAlcada[i].length; j++) {
        System.out.print(pesIAlcada[i][j]);
    }
}

I suggest you avoid using `float` not only does it make examples like this more complicated, but it has much less precision (it is one billion times less accurate) — Peter Lawrey, May 12 '13 at 10:52

flavian · Answer 1 · 2013-05-12T10:45:04.943

1

Use this function to deep-copy a 2d array.

public static float[][] deepCopy(float[][] original, Integer offset, Integer numberOfRows) {
    if (original == null) {
        return null;
    }
    if (offset == null) {
        offset = 0;
    };

    if (numberOfRows == null) {
        numberOfRows = original.length;
    };

    final float[][] result = new float[numberOfRows - offset][];
    for (int i = offset; i < numberOfRows; i++) {
         result[i] = Arrays.copyOf(original[i], original[i].length);
    }
    return result;
}

And in your code:

float[][] pesNeixement = deepCopy(pesIAlcada, 0, 2);

edited May 12 '13 at 10:45

answered May 12 '13 at 10:24

flavian

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I want to make a new Array called pesNeixement and take just these two rows for the new array(pesNeixement) .. { {2.4f, 3.1f, 3.07f, 3.7f, 2.7f, 2.9f, 3.2f, 3f, 3.6f, 3.1f}, {19f, 18.7f, 22f, 24f,17f, 18.5f, 21f, 20f, 18.7f, 22f, 18f}, – Muna Lisa May 12 '13 at 10:28
You might want to add an extra `offset` argument, in case someone wants to copy *x* rows starting at row *y*. – gkalpak May 12 '13 at 10:46
@alex23 the code is identical to this : http://stackoverflow.com/a/1564856/951448 And this answer is 3 years older than the question you're referring to ... – Mr.Me May 12 '13 at 10:50
@ alex23 Sorry I'm new here, how can I? – Muna Lisa May 12 '13 at 12:19

score 0 · Answer 2 · answered May 12 '13 at 10:22

0

It depends by your definition of "some information". If you want to copy a section of the array to a new one, then you can use System.arraycopy.

Example

int[] numbers = {4,5,6,7,8};
int[] newNumbers = new int[10];

System.arraycopy(numbers,0,newNumbers,0,3);

answered May 12 '13 at 10:22

christopher

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I want to make a new Array called pesNeixement and take just these two rows for the new array(pesNeixement) .. { {2.4f, 3.1f, 3.07f, 3.7f, 2.7f, 2.9f, 3.2f, 3f, 3.6f, 3.1f}, {19f, 18.7f, 22f, 24f,17f, 18.5f, 21f, 20f, 18.7f, 22f, 18f}, – Muna Lisa May 12 '13 at 10:31
So apply some reasoning, look at the answers you've been given and work out how you might get the top two lines. – christopher May 12 '13 at 10:32
Yes, i did here float[][] pesNeixement = new float[ROWS][COLS]; for (int i = 0; i < 2; i++) { for (int j = 0; j < pesIAlcada[i].length; j++) { System.out.print(pesIAlcada[i][j]); } } The problem is that how can i change the name from pesIAlcada to pesNeixement ?? – Muna Lisa May 12 '13 at 10:36

gkalpak · Answer 3 · 2013-05-13T05:21:02.187

If you want to copy some rows from pesIAlcada in an new array (pesNeixement) you can use something like this:

int fromRow = 0;     // Start copying at row0 (1st row)
int toRow = 2;       // Copy until row2 (3rd row) <- not included
                     // This will copy rows 0 and 1 (first two rows)
float[][] pesNeixement = new float[toRow - fromRow][];

for (int i = fromRow; i < toRow; i++) {
    pesNeixement[i] = new float[pesIAlcada[i].length];
    System.arraycopy(pesIAlcada[i], 0, pesNeixement[i], 0, pesIAlcada[i].length);               
}

Also see this short demo.

score 0 · Answer 4 · answered May 12 '13 at 10:51

0

System.arrayCopy() is the efficient way of creating new array from an existing array. What you can do with your own coding can be done using this also. Just explore

answered May 12 '13 at 10:51

K Adithyan

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How to make a new array from an old array?

4 Answers4