Python's statistics.mode in TypeScript

How to use

Install via yarn add locutus and import: import { mode } from 'locutus/python/statistics/mode'.

Or with CommonJS: const { mode } = require('locutus/python/statistics/mode')

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	mode([1, 1, 2, 2, 3])	1
2	mode(['red', 'blue', 'red', 'green'])	'red'
3	mode([true, false, true])	true

Notes

• Returns the first encountered most-common value.

Here's what our current TypeScript equivalent to Python's statistics.mode looks like.

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

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export function mode<T>(data: T[] | unknown): T {
  //      discuss at: https://locutus.io/python/statistics/mode/
  // parity verified: Python 3.12
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Returns the first encountered most-common value.
  //       example 1: mode([1, 1, 2, 2, 3])
  //       returns 1: 1
  //       example 2: mode(['red', 'blue', 'red', 'green'])
  //       returns 2: 'red'
  //       example 3: mode([true, false, true])
  //       returns 3: true

  const values = assertStatisticsArray(data, 'mode') as T[]
  if (values.length === 0) {
    throw new Error('no mode for empty data')
  }

  let bestValue = values[0] as T
  let bestCount = 0
  const counts = new Map<T, number>()

  for (const value of values) {
    const count = (counts.get(value) ?? 0) + 1
    counts.set(value, count)
    if (count > bestCount) {
      bestCount = count
      bestValue = value
    }
  }

  return bestValue
}

function assertStatisticsArray(data: unknown, functionName: string): unknown[] {
  if (!Array.isArray(data)) {
    throw new TypeError(`${functionName}() data must be an array`)
  }

  return data
}

export function mode(data) {
  //      discuss at: https://locutus.io/python/statistics/mode/
  // parity verified: Python 3.12
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Returns the first encountered most-common value.
  //       example 1: mode([1, 1, 2, 2, 3])
  //       returns 1: 1
  //       example 2: mode(['red', 'blue', 'red', 'green'])
  //       returns 2: 'red'
  //       example 3: mode([true, false, true])
  //       returns 3: true

  const values = assertStatisticsArray(data, 'mode')
  if (values.length === 0) {
    throw new Error('no mode for empty data')
  }

  let bestValue = values[0]
  let bestCount = 0
  const counts = new Map()

  for (const value of values) {
    const count = (counts.get(value) ?? 0) + 1
    counts.set(value, count)
    if (count > bestCount) {
      bestCount = count
      bestValue = value
    }
  }

  return bestValue
}

function assertStatisticsArray(data, functionName) {
  if (!Array.isArray(data)) {
    throw new TypeError(`${functionName}() data must be an array`)
  }

  return data
}

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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