@instructure/quiz-interactions/src/util/combinatorics.js

A React UI component Library for quiz interaction types.

import times from 'lodash/fp/times'
import concat from 'lodash/fp/concat'
import map from 'lodash/fp/map'
import reduce from 'lodash/fp/reduce'
import range from 'lodash/fp/range'
import flatten from 'lodash/fp/flatten'

export function identityMatrix([a = 1, b = 0], size) {
  return map(row => times(n => (n === row ? a : b), size), range(0, size))
}

// same concept as https://github.com/dankogai/js-combinatorics#cartesian-product
export function cartesianProduct(...arrays) {
  return reduce((a, b) => flatten(map(x => map(y => concat(x, [y]), b), a)), [[]], arrays)
}

// same concept as https://github.com/dankogai/js-combinatorics#base-n
export function baseNCombination(values, n) {
  if (n === 0) {
    return []
  }

  if (n === 1) {
    return map(v => [v], values)
  }

  const previous = baseNCombination(values, n - 1)
  return cartesianProduct(values, previous).map(([v, p]) => [v, ...p])
}

// same concept as https://github.com/dankogai/js-combinatorics#combination
export function combination(array, size) {
  if (size === 0) {
    return []
  }

  if (size === 1) {
    return map(v => [v], array)
  }

  if (array.length === 1) {
    return [times(() => array[0], size)]
  }

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

  return concat(
    map(v => [array[0], ...v], combination(array, size - 1)),
    combination(array.slice(1), size),
  )
}