How to get 2D subarray from 2D array in JAVA?

Question

Suppose I have 2D array as follow:

int[][] temp={
              {1,2,3,4},
              {5,6,7,8},
              {9,10,11,12}};

and i want to get sub-array start from X direction 1 to 2 and Y direction 1 to 2 ie

{6,7}
{10,11}

can anyone give me solution for above problem.

Answer 1

Here you are

    int[][] temp = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } };
    int[][] a = new int[temp.length][];
    for (int i = 0; i < temp.length; i++) {
        a[i] = Arrays.copyOfRange(temp[i], 1, 3);
    }
    System.out.println(Arrays.deepToString(a));

output

[[2, 3], [6, 7], [10, 11]]

answering your question in comment if we want to access only [[6, 7], [10, 11]]

    int[][] a = new int[2][];
    for (int i = 1, j = 0; i < 3; i++, j++) {
        a[j] = Arrays.copyOfRange(temp[i], 1, 3);
    }

output

[[6, 7], [10, 11]]

Answer 2

As an example without using the Arrays class:

int[][] temp = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } };
int[][] subArray = new int[temp.length][];
for (int i = 0; i < subArray.length; i++) {
    subArray[i] = new int[2];
    subArray[i][0] = temp[i][1];
    subArray[i][1] = temp[i][2];
}

You can then access any part of subArray that you want. This will access the values [[6, 7], [10, 11]]:

for (int x = 1; x < 3; x++) {
    System.out.println(subArray[x][0]);
    System.out.println(subArray[x][1]);
}

[Additional] To address the modified question:

If you want to create a smaller array you can play around with the start and end points of the loop, and the indices accessed within the loop, for example this will create the array you ask for:

int[][] subArray = new int[2][];
for (int i = 1; i < temp.length; i++) {
    subArray[i-1] = new int[2];
    subArray[i-1][0] = temp[i][1];
    subArray[i-1][1] = temp[i][2];
}

Answer 3

Just adding a little bit to the accepted answer.

You can make a static method to generalize it for all 2D arrays with fixed width and height

public static char[][] get2DSubArray(char[][] origArray, int fromRow, int toRow, int fromColumn, int toColumn) {
    char[][] subArray = new char[toColumn - fromColumn][];
    
    for (int i = fromColumn; i < toColumn; i++) {
        subArray[i - fromColumn] = Arrays.copyOfRange(origArray[i], fromRow, toRow);
    }
    
    return subArray;
}

Hope this can help too!

Answer 4

您可以实例化一个新数组并循环遍历原始数组的适当索引以初始化子数组。