1 answers

3 points

Asked by:

178290

How to transpose matrix in java?

I have:

xxxxxxxxxx
 
int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

And I expect:

xxxxxxxxxx
 
int[][] transposed = {
    {1, 4, 7},
    {2, 5, 8},
    {3, 6, 9}
};

1 answer

3 points

Answered by:

Root-ssh

178290

Quick solution (it works for square and rectangular matrixes) :

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public static int[][] transposeMatrix(int[][] matrix) {
​
    int[][] temporary = new int[matrix[0].length][matrix.length];
​
    for (int i = 0; i < matrix.length; i++) {
        for (int j = 0; j < matrix[0].length; j++) {
            temporary[j][i] = matrix[i][j];
        }
    }
    return temporary;
}

Example 1

Below example transpose square matrix of size 3 x 3 (3 rows, 3 columns), with total 9 elements. Transposition logic is the same as in quick solution above.

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import java.util.Arrays;
​
public class TransposeMatrix {
​
    public static int[][] transposeMatrix(int[][] matrix) {
        int[][] temporary = new int[matrix[0].length][matrix.length];
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                temporary[j][i] = matrix[i][j];
            }
        }
        return temporary;
    }
​
    public static void main(String[] args) {
        int[][] matrix = {
                {1, 2, 3},
                {4, 5, 6},
                {7, 8, 9}
        };
        System.out.println("# matrix before transposition:");
        for (int[] row : matrix) {
            System.out.println(Arrays.toString(row));
        }
        int[][] transposed = transposeMatrix(matrix);
        System.out.println("# matrix after transposition:");
        for (int[] row : transposed) {
            System.out.println(Arrays.toString(row));
        }
    }
}

Output:

xxxxxxxxxx
 
# matrix before transposition:
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
# matrix after transposition:
[1, 4, 7]
[2, 5, 8]
[3, 6, 9]

Example 2

Below example transpose rectangular matrix of size 2 x 4 (2 rows, 4 columns), with total 8 elements. Transposition logic is the same. We only change the input matrix.

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import java.util.Arrays;
​
public class TransposeMatrix2 {
​
    public static int[][] transposeMatrix(int[][] matrix) {
        int[][] temporary = new int[matrix[0].length][matrix.length];
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                temporary[j][i] = matrix[i][j];
            }
        }
        return temporary;
    }
​
    public static void main(String[] args) {
        int[][] matrix = {
                {1, 2, 3, 4},
                {5, 6, 7, 8}
        };
        System.out.println("# matrix before transposition:");
        for (int[] row : matrix) {
            System.out.println(Arrays.toString(row));
        }
        int[][] transposed = transposeMatrix(matrix);
        System.out.println("# matrix after transposition:");
        for (int[] row : transposed) {
            System.out.println(Arrays.toString(row));
        }
    }
}

Output:

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# matrix before transposition:
[1, 2, 3, 4]
[5, 6, 7, 8]
# matrix after transposition:
[1, 5]
[2, 6]
[3, 7]
[4, 8]

Some details

In math, transpose of matrix is the process of chaning rows to columns and columns to rows. The process of transposition is quite easy, we just change A[i][j] to A[j][i].
We can do it in couple of different ways.
It is very oftne used in linear algebra.

Wikipedia has quite solid articles about this topic.

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Java transpose matrix

Example 1

Example 2

Some details

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