How to multiply n arrays of the same length with each other?

July 18, 2023

I want to multiply arrays of the same length. The total number of arrays (input.length) is known, but it can be everything between 0 and n.

const input = [
  [1, 2, 3, 4],
  [1, 2, 3, 4],
  [1, 2, 3, 4],
  [1, 2, 3, 4]
];

const output = [1, 16, 81, 256];
// 1*1*1*1, 2*2*2*2, 3*3*3*3, 4*4*4*4

I found solutions on SO for multiplying two arrays by mapping them against each other, but not for n arrays.

I am grateful for any hints.

>Solution :

If you want to multiply arrays, the best solution would be the Array#Reduce function

You here only need to introduce a function as I did with multiplyArray to handle how to compute to arrays together

const input = [
  [1, 2, 3, 4],
  [1, 2, 3, 4],
  [1, 2, 3, 4],
  [1, 2, 3, 4]
];

const multiplyArray = (arr1, arr2) => {
  if(arr1.length !== arr2.length) {
    throw new Error('Array have not the same length');
  }
  
  arr1.forEach((elem, index) => {
    arr1[index] = elem * arr2[index]
  })
  
  return arr1
}

const output = input.reduce((acc, curr) => {
  if(acc === null) return curr
  
  return multiplyArray(acc, curr)
}, null)

console.log(output)