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TypeScript - transpose matrix

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Created by:

Dollie-Rutledge

806

In this short article, we would like to show how to transpose a matrix in TypeScript.

Quick solution:

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const transposeMatrix = (matrix: number[][]): number[][] => {
  const result = new Array(matrix.length);
  for (let i = 0; i < matrix.length; ++i) {
    result[i] = new Array(matrix[0].length);
  }
  for (let i = 0; i < matrix.length; ++i) {
    for (let j = 0; j < matrix[0].length; ++j) {
      result[j][i] = matrix[i][j];
    }
  }
  return result;
};
​
// Helper methods:
​
const printMatrix = (matrix: number[][]): void => {
  let text = '';
  for (let i = 0; i < matrix.length; ++i) {
    const row = matrix[i];
    for (let j = 0; j < row.length; ++j) {
      text += row[j] + ' ';
    }
    text += '\n';
  }
  console.log(text);
};
​
​
// Usage example:
​
const matrix: number[][] = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];
const transposedMatrix: number[][] = transposeMatrix(matrix);
​
printMatrix(transposedMatrix);  // 1 4 7
                                // 2 5 8
                                // 3 6 9

Note: above example do not check sizes of arrays.

Matrix transposition with sizes checking example

Edit

The solution presented in this section checks each row size and informs if transposition can not be done.

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const createMatrix = (width: number, height: number): number[][] => {
  const result = new Array(height);
  for (let i = 0; i < height; ++i) {
    result[i] = new Array(width);
  }
  return result;
};
​
const transposeMatrix = (matrix: number[][]): number[][] => {
  if (matrix.length == 0) {
    return [];
  }
  const matrixRow = matrix[0];
  if (matrixRow == null) {
    throw new Error('Undefined matrix row 1.');
  }
  const matrixWidth = matrixRow.length;
  const matrixHeight = matrix.length;
  const result = createMatrix(matrixWidth, matrixHeight);
  for (let i = 0; i < matrixHeight; ++i) {
    const matrixRow = matrix[i];
    if (matrixRow == null) {
      throw new Error('Undefined matrix row ' + (i + 1) + '.');
    }
    if (matrixWidth != matrixRow.length) {
      throw new Error('Matrix row ' + (i + 1) + ' has different width than row 1.');
    }
    for (let j = 0; j < matrixWidth; ++j) {
      result[j][i] = matrixRow[j];
    }
  }
  return result;
};
​
// Helper methods:
​
const printMatrix = (matrix: number[][]): void => {
  let text = '';
  for (let i = 0; i < matrix.length; ++i) {
    const row = matrix[i];
    for (let j = 0; j < row.length; ++j) {
      text += row[j] + ' ';
    }
    text += '\n';
  }
  console.log(text);
};
​
​
// Usage example:
​
const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];
const transposedMatrix = transposeMatrix(matrix);
​
printMatrix(transposedMatrix); // 1 4 7
                               // 2 5 8
                               // 3 6 9