Multiply 2 matrices in Javascript

Question

I\'m doing a function that multiplies 2 matrices. The matrices will always have the same number of rows and columns. (2x2, 5x5, 23x23, ...)

When I print it, it doesn

Answer 1

Here's my ES6 soulution with math error handling:

const matrixDot = (A, B) => {
  // Math error handling
  const matrices = [A, B];
  const cols = matrices.map((item) => item[0].length);
  if (!matrices.every((item, i) => item.every((row) => row.length === cols[i])))
    return console.error('All rows in a matrix must have equal amount of columns');
  else if (cols[0] !== B.length)
    return console.error(
      'Amount of columns in the 1st matrix must match amount of rows in the 2nd matrix'
    );
  // Calculations
  return A.map((rowA) =>
    B[0].map((_, colBIndex) =>
      rowA.reduce((acc, itemA, rowBIndex) => acc + itemA * B[rowBIndex][colBIndex], 0)
    )
  );
};

// Example
const A = [
  [3, 2, 5],
  [6, 4, 1],
];
const B = [
  [2, 6],
  [5, 3],
  [1, 4],
];
console.log(matrixDot(A, B));
// [ [21, 44],
//   [33, 52] ]

Here's gist if you want to bookmark it

Hope it helps somebody ;)