Question 210220 in Javascript Question posted in
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Javascript – How to multiply n arrays of the same length with each other?

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.

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3

Answers


  1. 0

    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)
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  2. 0 
    const input = [
  [1, 2, 3, 4],
  [1, 2, 3, 4],
  [1, 2, 3, 4],
  [1, 2, 3, 4]
]

const result = input.reduce((filtered, current) => {
  filtered.push(current.reduce((accumulator, currNum) => {
    accumulator.push(Math.pow(currNum, input.length))
    return accumulator
  }, []))

  return filtered
}, [])
    
console.log(result)
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  3. 0

    You can use Array.prototype.map() combined with Array.prototype.reduce() and Array.prototype.every() to create a function multiplyAcrossArrays with validation to check length of sub-arrays

    Code:

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

const multiplyAcrossArrays = (input) => {
  if (!input.every(subArray => subArray.length === input[0].length)) {
    throw new Error('All sub-arrays must have the same length')
  }

  return input[0].map((_, i) => input.reduce((a, c) => a * c[i], 1))
}

console.log(multiplyAcrossArrays(input))
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