Write Java method which merge two 2D Arrays into 1 2D Array

Question

I am looking for a method which will merge two 2D arrays into one 2D array.

Arrays may store any types of data.

For example I have:

Object[][] dataProvider = new Object[][]{
                {12, 6.0}, {6, 3.0}
        };

Object[][] impl = new Object[][]{
                {1}, {2}, {3}
        };

As a result should be array below:

Object[][] result = new Object[][]{

{1, 12, 6.0}
{1, 6, 3.0}
{2, 12, 6.0}
{2, 6, 3.0}
{3, 12, 6.0}
{3, 6, 3.0}

 };

here is my code:

public Object[][] merge(Object[][] impl, Object[][] dataProvider) {
        int n = dataProvider.length;
        int m = impl.length;

        Object[][] merged = new Object[m * n][];
        int countLines = 0;

        for (Object[] objects : impl) {
            for (Object[] value : dataProvider) {
                int g = objects.length + value.length;
                List<Object> list = new ArrayList<>();

                for (int j = 0; j < objects.length; j++) {
                    list.add(j, impl[j]);
                }

                for (int k = 0; k < value.length; k++) {
                    list.add(list.size(), value);
                }

                merged[countLines] = list.toArray();
                countLines++;
                list.clear();
            }
        }
        return merged;
    }

The output for merge[0] is [1], [12, 6.0], [12, 6.0] The output should be [1, 12, 6.0]

Could you please help me to find a mistake in the method? Thanks ahead!

In other words, what's wrong with your current code? Are you getting the wrong output (if yes, what)? An exception (if yes, what and where)? Something else? — Federico klez Culloca
– Federico klez Culloca, Commented Jul 8, 2022 at 19:21
when I try to print merged[0][1] element I got [12, 6.0] instead of [12] — Myroslava Vynokur
– Myroslava Vynokur, Commented Jul 8, 2022 at 19:24
@MyroslavaVynokur please edit your question to include that piece of information. It's an integral part of your question, so it belongs there, not in comments. — Federico klez Culloca
– Federico klez Culloca, Commented Jul 8, 2022 at 19:28
By the way, how are you printing it? Printing a specific index of a 2-dimensinal array shouldn't print an array. — Federico klez Culloca
– Federico klez Culloca, Commented Jul 8, 2022 at 19:28

WJS · Accepted Answer · 2022-07-08 21:32:06Z

1

Using a combination of loops and stream this will merge the two as requested.

Object[][] dataProvider =
        new Object[][] { { 12, 6.0 }, { 6, 3.0 } };
Object[][] impl = new Object[][] { { 1 }, { 2 }, { 3 } };

Object[][] result = merge(impl, dataProvider);

for (Object[] arr : result) {
    System.out.println(Arrays.toString(arr));
}

prints

[1, 12, 6.0]
[1, 6, 3.0]
[2, 12, 6.0]
[2, 6, 3.0]
[3, 12, 6.0]
[3, 6, 3.0]

This will allow the first and second arrays to be merges as described above. Any type is supported.

compute the length of the resultant array
Allocate a result array
stream the two arrays and assign to the appropriate array.
return the result.

@SuppressWarnings("unchecked")
public static <T> T[][] merge(T[][] first, T[][] second) {
    int rows = first.length * second.length;
    T[][] result = (T[][]) new Object[rows][];
    int r = 0;
    for (T[] arr : first) {
        for (T[] arr2 : second) {
            result[r++] = (T[]) Stream.of(arr, arr2)
                    .flatMap(Arrays::stream).toArray();
        }
    }
    return result;
}

edited Jul 8, 2022 at 21:32

answered Jul 8, 2022 at 21:19

WJS

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1 Comment

Myroslava Vynokur Over a year ago

many thanks for the answer! I will try to simplify my code according to your suggestion, thanks!

Eritrean · Accepted Answer · 2022-07-08 20:24:56Z

You could just concat the rows of your arrays using copy methods:

import java.util.Arrays;

public class Example {

    public static void main(String[] args) {

        Object[][] impl = {{1}, {2}, {3}};

        Object[][] dataProvider = {{12, 6.0}, {6, 3.0}};

        System.out.println(Arrays.deepToString(merge(impl, dataProvider)));
    }

    public static Object[][] merge(Object[][] impl, Object[][] dataProvider) {
        int n = dataProvider.length;
        int m = impl.length;

        Object[][] merged = new Object[m * n][];
        int row = 0;

        for (Object[] objects : impl) {
            for (Object[] value : dataProvider) {
                merged[row++] = concatArrays(objects, value);
            }
        }

        return merged;
    }

    static Object[] concatArrays(Object[] array1, Object[] array2) {
        Object[] result = Arrays.copyOf(array1, array1.length + array2.length);
        System.arraycopy(array2, 0, result, array1.length, array2.length);
        return result;
    }
}

output:

[[1, 12, 6.0], [1, 6, 3.0], [2, 12, 6.0], [2, 6, 3.0], [3, 12, 6.0], [3, 6, 3.0]]

kulity · Accepted Answer · 2022-07-09 05:22:38Z

0

The main mistake is that your method's code is very difficult.

Let me introduce you to my solution

    Object[][] merge(Object[][] array1, Object[][] array2) {
        Object[][] result = new Object[array1.length * array2.length][];
        for(int i = 0; i < array1.length; ++i)
            for (int j = 0; j < array2.length; ++j) {
                result[i * array2.length + j] = merge(array1[i], array2[j]);
            }
        return result;
    }

    Object[] merge(Object[] array1, Object[] array2) {
        return Stream.of(array1, array2)
                .flatMap(Stream::of)
                .toArray(Object[]::new);
    }

merge(impl, dataProvider) gives exactly what you want

edited Jul 9, 2022 at 5:22

answered Jul 9, 2022 at 4:29

kulity

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2 Comments

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

Myroslava Vynokur Over a year ago

many thanks! it really looks much simpler, thanks again!

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