pickRandom.js

import { flatten } from '../../utils/array.js'
import { factory } from '../../utils/factory.js'
import { isMatrix, isNumber } from '../../utils/is.js'
import { createRng } from './util/seededRNG.js'

const name = 'pickRandom'
const dependencies = ['typed', 'config', '?on']

export const createPickRandom = /* #__PURE__ */ factory(name, dependencies, ({ typed, config, on }) => {
  // seeded pseudo random number generator
  let rng = createRng(config.randomSeed)

  if (on) {
    on('config', function (curr, prev) {
      if (curr.randomSeed !== prev.randomSeed) {
        rng = createRng(curr.randomSeed)
      }
    })
  }

  /**
   * Random pick one or more values from a one dimensional array.
   * Array elements are picked using a random function with uniform or weighted distribution.
   *
   * Syntax:
   *
   *     math.pickRandom(array)
   *     math.pickRandom(array, number)
   *     math.pickRandom(array, weights)
   *     math.pickRandom(array, number, weights)
   *     math.pickRandom(array, weights, number)
   *     math.pickRandom(array, { weights, number, elementWise })
   *
   * Examples:
   *
   *     math.pickRandom([3, 6, 12, 2])                  // returns one of the values in the array
   *     math.pickRandom([3, 6, 12, 2], 2)               // returns an array of two of the values in the array
   *     math.pickRandom([3, 6, 12, 2], { number: 2 })   // returns an array of two of the values in the array
   *     math.pickRandom([3, 6, 12, 2], [1, 3, 2, 1])    // returns one of the values in the array with weighted distribution
   *     math.pickRandom([3, 6, 12, 2], 2, [1, 3, 2, 1]) // returns an array of two of the values in the array with weighted distribution
   *     math.pickRandom([3, 6, 12, 2], [1, 3, 2, 1], 2) // returns an array of two of the values in the array with weighted distribution
   *
   *     math.pickRandom([{x: 1.0, y: 2.0}, {x: 1.1, y: 2.0}], { elementWise: false })
   *         // returns one of the items in the array
   *
   * See also:
   *
   *     random, randomInt
   *
   * @param {Array | Matrix} array     A one dimensional array
   * @param {Int} number               An int or float
   * @param {Array | Matrix} weights   An array of ints or floats
   * @return {number | Array}          Returns a single random value from array when number is 1 or undefined.
   *                                   Returns an array with the configured number of elements when number is > 1.
   */
  return typed(name, {
    'Array | Matrix': function (possibles) {
      return _pickRandom(possibles, {})
    },

    'Array | Matrix, Object': function (possibles, options) {
      return _pickRandom(possibles, options)
    },

    'Array | Matrix, number': function (possibles, number) {
      return _pickRandom(possibles, { number })
    },

    'Array | Matrix, Array | Matrix': function (possibles, weights) {
      return _pickRandom(possibles, { weights })
    },

    'Array | Matrix, Array | Matrix, number': function (possibles, weights, number) {
      return _pickRandom(possibles, { number, weights })
    },

    'Array | Matrix, number, Array | Matrix': function (possibles, number, weights) {
      return _pickRandom(possibles, { number, weights })
    }
  })

  /**
   * @param {Array | Matrix} possibles
   * @param {{
   *   number?: number,
   *   weights?: Array | Matrix,
   *   elementWise: boolean
   * }} options
   * @returns {number | Array}
   * @private
   */
  function _pickRandom (possibles, { number, weights, elementWise = true }) {
    const single = (typeof number === 'undefined')
    if (single) {
      number = 1
    }

    const createMatrix = isMatrix(possibles)
      ? possibles.create
      : isMatrix(weights)
        ? weights.create
        : null

    possibles = possibles.valueOf() // get Array
    if (weights) {
      weights = weights.valueOf() // get Array
    }

    if (elementWise === true) {
      possibles = flatten(possibles)
      weights = flatten(weights)
    }

    let totalWeights = 0

    if (typeof weights !== 'undefined') {
      if (weights.length !== possibles.length) {
        throw new Error('Weights must have the same length as possibles')
      }

      for (let i = 0, len = weights.length; i < len; i++) {
        if (!isNumber(weights[i]) || weights[i] < 0) {
          throw new Error('Weights must be an array of positive numbers')
        }

        totalWeights += weights[i]
      }
    }

    const length = possibles.length

    const result = []
    let pick

    while (result.length < number) {
      if (typeof weights === 'undefined') {
        pick = possibles[Math.floor(rng() * length)]
      } else {
        let randKey = rng() * totalWeights

        for (let i = 0, len = possibles.length; i < len; i++) {
          randKey -= weights[i]

          if (randKey < 0) {
            pick = possibles[i]
            break
          }
        }
      }

      result.push(pick)
    }

    return single
      ? result[0]
      : createMatrix
        ? createMatrix(result)
        : result
  }
})