Python's statistics.median in TypeScript

✓ Verified: Python 3.12

How to use

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

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

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	`median([1, 3, 5])`	`3`
2	`median([1, 2, 3, 4])`	`2.5`
3	`median(['b', 'a', 'c'])`	`'b'`

Notes

Returns the middle data point, averaging the two middle numeric points for even-length input.

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

export function median(data: unknown): number | string | boolean | bigint {
  //      discuss at: https://locutus.io/python/statistics/median/
  // parity verified: Python 3.12
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Returns the middle data point, averaging the two middle numeric points for even-length input.
  //       example 1: median([1, 3, 5])
  //       returns 1: 3
  //       example 2: median([1, 2, 3, 4])
  //       returns 2: 2.5
  //       example 3: median(['b', 'a', 'c'])
  //       returns 3: 'b'

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

  const middleIndex = Math.floor(values.length / 2)
  if (values.length % 2 === 1) {
    return values[middleIndex] as number | string | boolean | bigint
  }

  const left = values[middleIndex - 1]
  const right = values[middleIndex]
  if (typeof left === 'string' || typeof right === 'string') {
    throw new TypeError("unsupported operand type(s) for /: 'str' and 'int'")
  }

  return (toStatisticNumber(left, 'median') + toStatisticNumber(right, 'median')) / 2
}

type StatisticsSortableInput = number | boolean | bigint | string

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

  if (data.length === 0) {
    return []
  }

  const values = data as StatisticsSortableInput[]
  const firstKind = getStatisticsSortKind(values[0], functionName)
  for (let index = 1; index < values.length; index += 1) {
    if (getStatisticsSortKind(values[index], functionName) !== firstKind) {
      throw new TypeError(`${functionName}() requires data values that can be ordered together`)
    }
  }

  return [...values].sort((left, right) => compareStatisticsValues(left, right, firstKind))
}

function toStatisticNumber(value: unknown, functionName: string): number {
  if (typeof value === 'number') {
    return value
  }

  if (typeof value === 'boolean') {
    return value ? 1 : 0
  }

  if (typeof value === 'bigint') {
    const numericValue = Number(value)
    if (!Number.isSafeInteger(numericValue)) {
      throw new RangeError(`${functionName}() bigint values must fit within JS safe integers`)
    }

    return numericValue
  }

  throw new TypeError(`${functionName}() data must contain only real numbers`)
}

function getStatisticsSortKind(value: unknown, functionName: string): 'number' | 'string' {
  if (typeof value === 'string') {
    return 'string'
  }

  if (typeof value === 'number' || typeof value === 'boolean' || typeof value === 'bigint') {
    return 'number'
  }

  throw new TypeError(`${functionName}() requires sortable scalar values`)
}

function compareStatisticsValues(
  left: StatisticsSortableInput,
  right: StatisticsSortableInput,
  kind: 'number' | 'string',
): number {
  if (kind === 'string') {
    return String(left).localeCompare(String(right))
  }

  return toNumericSortValue(left) - toNumericSortValue(right)
}

function toNumericSortValue(value: StatisticsSortableInput): number {
  return typeof value === 'boolean' ? (value ? 1 : 0) : Number(value)
}

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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