Python's math.prod in TypeScript

✓ Verified: Python 3.12

Rosetta Stone: php/array_product

How to use

Install via yarn add locutus and import: import { prod } from 'locutus/python/math/prod'.

Or with CommonJS: const { prod } = require('locutus/python/math/prod')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	`prod([2, 3, 4])`	`24`
2	`prod([], 5)`	`5`
3	`prod([1.5, 2, 3], 2)`	`18`

Notes

Multiplies all iterable values together and applies the optional start value first.

Here's what our current TypeScript equivalent to Python's math.prod looks like.

type ProdValue = number | string

export function prod(values: ProdValue[] | unknown, start: ProdValue = 1): ProdValue {
  //      discuss at: https://locutus.io/python/prod/
  // parity verified: Python 3.12
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Multiplies all iterable values together and applies the optional start value first.
  //       example 1: prod([2, 3, 4])
  //       returns 1: 24
  //       example 2: prod([], 5)
  //       returns 2: 5
  //       example 3: prod([1.5, 2, 3], 2)
  //       returns 3: 18

  if (!Array.isArray(values)) {
    throw new TypeError('prod(): iterable must be an array')
  }

  let result: ProdValue = start
  for (const value of values) {
    result = multiplyProdValues(result, value)
  }

  return result
}

function multiplyProdValues(left: ProdValue, right: ProdValue): ProdValue {
  if (typeof left === 'string' && typeof right !== 'string') {
    return repeatString(left, right)
  }

  if (typeof right === 'string' && typeof left !== 'string') {
    return repeatString(right, left)
  }

  if (typeof left !== 'number' || typeof right !== 'number') {
    throw new TypeError('prod(): values must be numbers or repeatable strings')
  }

  const leftNumber = left
  const rightNumber = right

  if (Number.isInteger(leftNumber) && Number.isInteger(rightNumber)) {
    if (leftNumber === 0 || rightNumber === 0) {
      return 0
    }
    if (leftNumber === 1) {
      return rightNumber
    }
    if (rightNumber === 1) {
      return leftNumber
    }
    if (leftNumber === -1) {
      return -rightNumber
    }
    if (rightNumber === -1) {
      return -leftNumber
    }

    if (!Number.isSafeInteger(leftNumber) || !Number.isSafeInteger(rightNumber)) {
      throw new RangeError('prod(): integer multiplication only supports JS safe integers')
    }

    const result = leftNumber * rightNumber
    if (!Number.isSafeInteger(result)) {
      throw new RangeError('prod(): integer multiplication only supports JS safe integers')
    }

    return result
  }

  return leftNumber * rightNumber
}

function repeatString(value: string, multiplier: ProdValue): string {
  if (typeof multiplier !== 'number') {
    throw new TypeError('prod(): string repetition requires a safe integer multiplier')
  }

  const count = multiplier
  if (!Number.isInteger(count) || !Number.isSafeInteger(count)) {
    throw new TypeError('prod(): string repetition requires a safe integer multiplier')
  }

  return count > 0 ? value.repeat(count) : ''
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

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Help us add more

Got a rainy Sunday afternoon and a taste for a porting puzzle?

Get inspiration from the Python 3 standard library string page.
Click "New file" in the appropriate folder on GitHub. This will fork the project to your account, directly add the file to it, and send a Pull Request to us.

We will then review it. If it's useful to the project and in line with our contributing guidelines your work will become part of Locutus and you'll be automatically credited in the authors section accordingly.

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