Pandemonium

Pandemonium is a dead simple JavaScript/TypeScript library providing typical random-related functions such as choice, sample etc.

The library also provides a way to create any of the available functions using a custom random source (seedrandom, for instance).

Installation

npm install --save pandemonium

Usage

Summary

Typical helpers

choice
random
randomBoolean
randomFloat
randomIndex
randomString
randomUint32
randomPair
randomOrderedPair
shuffle
shuffleInPlace
weightedChoice
weightedRandomIndex

Sampling

n being the number of items in the sampled sequence and k being the number of items to be sampled.

Method	Time	Memory	Note
dangerouslyMutatingSample	`O(k)`	`O(k)`	Must be able to mutate given array to work.
fisherYatesSample	`O(n)`	`O(n)`	Probably not a good idea.
geometricReservoirSample	`O(k*log(n/k))`	`O(k)`	Probably the best way of sampling from a random access data structure.
naiveSample	`Ω(k)`, `O(∞)`	`O(k)`	Only useful if `k << n`.
reservoirSample	`O(n)`	`O(k)`	Useful if pulling a sample from a stream.
sampleWithReplacements	`O(k)`	`O(k)`	Performant but allows replacements.
samplePairs	`Ω(k)`, `O(∞)`	`O(k)`	Variant of naiveSample for unordered pairs.
sampleOrderedPairs	`Ω(k)`, `O(∞)`	`O(k)`	Variant of naiveSample for ordered pairs.
weightedReservoirSample	`O(n)`	`O(k)`	Variant of reservoirSample working with weighted items.

choice

Function returning a random item from the given array.

import choice from 'pandemonium/choice';
// Or
import {choice} from 'pandemonium';

choice(['apple', 'orange', 'pear']);
>>> 'orange'

// To create your own function using custom RNG
import {createChoice} from 'pandemonium/choice';

const customChoice = createChoice(rng);

random

Function returning a random integer between given a & b.

import random from 'pandemonium/random';
// Or
import {random} from 'pandemonium';

random(3, 7);
>>> 4

// To create your own function using custom RNG
import {createRandom} from 'pandemonium/random';

const customRandom = createRandom(rng);

randomBoolean

Function returning a random boolean.

import randomBoolean from 'pandemonium/random-boolean';
// Or
import {randomBoolean} from 'pandemonium';

randomBoolean();
>>> true

// To create your own function using custom RNG
import {createrandomBoolean} from 'pandemonium/random-boolean';

const customRandomBoolean = createRandomBoolean(rng);

randomFloat

Function returning a random float between given a & b.

import randomFloat from 'pandemonium/random-float';
// Or
import {randomFloat} from 'pandemonium';

randomFloat(-5, 55);
>>> 6.756482

// To create your own function using custom RNG
import {createRandomFloat} from 'pandemonium/random-float';

const customRandomFloat = createRandomFloat(rng);

randomIndex

Function returning a random index of the given array.

import randomIndex from 'pandemonium/random-index';
// Or
import {randomIndex} from 'pandemonium';

randomIndex(['apple', 'orange', 'pear']);
>>> 1

// Alternatively, you can give the array's length instead
randomIndex(3);
>>> 2

// To create your own function using custom RNG
import {createRandomIndex} from 'pandemonium/random-index';

const customRandomIndex = createRandomIndex(rng);

randomString

Function returning a random string.

import randomString from 'pandemonium/random-string';
// Or
import {randomString} from 'pandemonium';

// To generate a string of fixed length
randomString(5);
>>> 'gHepM'

// To generate a string of variable length
randomString(3, 7);
>>> 'hySf3'

// To create your own function using custom RNG
import {createRandomString} from 'pandemonium/random-string';

const customRandomString = createRandomString(rng);

// If you need a custom alphabet
const customRandomString = createRandomString(rng, 'ATGC');

randomUint32

Function returning a random unsigned 32bits number.

import {randomUint32} from 'pandemonium/random-typed-int';
// Or
import {randomUint32} from 'pandemonium';

randomUint32();
>>> 397536

// To create your own function using custom RNG
import {createRandomUint32} from 'pandemonium/random-typed-int';

const customRandomUint32 = createRandomUint32(rng);

randomPair

Function returning a random pair from the given array.

Note that this function will return unordered pairs (i.e. [0, 1] and [1, 0] are to be considered the same) and will not return pairs containing twice the same item (i.e. [0, 0]).

import randomPair from 'pandemonium/random-pair';
// Or
import {randomPair} from 'pandemonium';

randomPair(['apple', 'orange', 'pear', 'cherry']);
>>> ['orange', 'cherry']

// Alternatively, you can give the array's length instead and get a pair of indices
randomPair(4);
>>> [1, 3]

// To create your own function using custom RNG
import {createRandomPair} from 'pandemonium/random-pair';

const customRandomPair = createRandomPair(rng);

randomOrderedPair

Function returning a random ordered pair (i.e. [0, 1] won't be considered to be the same as [1, 0]) from the given array.

import randomOrderedPair from 'pandemonium/random-ordered-pair';
// Or
import {randomOrderedPair} from 'pandemonium';

randomOrderedPair(['apple', 'orange', 'pear', 'cherry']);
>>> ['cherry', 'apple']

// Alternatively, you can give the array's length instead and get a pair of indices
randomOrderedPair(4);
>>> [3, 0]

// To create your own function using custom RNG
import {createRandomOrderedPair} from 'pandemonium/random-ordered-pair';

const customRandomPair = createRandomOrderedPair(rng);

shuffle

Function returning a shuffled version of the given array using the Fisher-Yates algorithm.

If what you need is to shuffle the original array in place, check out shuffleInPlace.

import shuffle from 'pandemonium/shuffle';
// Or
import {shuffle} from 'pandemonium';

shuffle(['apple', 'orange', 'pear', 'pineapple']);
>>> ['pear', 'orange', 'apple', 'pineapple']

// To create your own function using custom RNG
import {createShuffle} from 'pandemonium/shuffle';

const customShuffle = createShuffle(rng);

shuffleInPlace

Function shuffling the given array in place using the Fisher-Yates algorithm.

import shuffleInPlace from 'pandemonium/shuffle-in-place';
// Or
import {shuffleInPlace} from 'pandemonium';

const array = ['apple', 'orange', 'pear', 'pineapple'];
shuffleInPlace(array);

// Array was mutated:
array >>> ['pear', 'orange', 'apple', 'pineapple'];

// To create your own function using custom RNG
import {createShuffleInPlace} from 'pandemonium/shuffle-in-place';

const customShuffleInPlace = createShuffleInPlace(rng);

weightedChoice

Function returning a random item from the given array of weights.

Note that weights don't need to be relative.

import weightedChoice from 'pandemonium/weighted-choice';
// Or
import {weightedChoice} from 'pandemonium';

const array = [.1, .1, .4, .3, .1];
weightedChoice(array);
>>> .4

// To create your own function using custom RNG
import {createWeightedChoice} from 'pandemonium/weighted-choice';

const customWeightedChoice = createWeightedChoice(rng);

// If you have an array of objects
const customWeightedChoice = createWeightedChoice({
  rng: rng,
  getWeight: (item, index) => {
    return item.weight;
  }
});

const array = [{fruit: 'pear', weight: 4}, {fruit: 'apple', weight: 30}];
customWeightedChoice(array);
>>> 'apple'


// If you intent to call the function multiple times on the same array,
// you should use the cached version instead:
import {createCachedWeightedChoice} from 'pandemonium/weighted-choice';

const array = [.1, .1, .4, .3, .1];
const customWeightedChoice = createCachedWeightedChoice(rng, array);

customWeightedChoice();
>>> .3

weightedRandomIndex

Function returning a random index from the given array of weights.

Note that weights don't need to be relative.

import weightedRandomIndex from 'pandemonium/weighted-random-index';
// Or
import {weightedRandomIndex} from 'pandemonium';

const array = [.1, .1, .4, .3, .1];
weightedRandomIndex(array);
>>> 2

// To create your own function using custom RNG
import {createWeightedRandomIndex} from 'pandemonium/weighted-random-index';

const customWeightedRandomIndex = createWeightedRandomIndex(rng);

// If you have an array of objects
const customWeightedRandomIndex = createWeightedRandomIndex({
  rng: rng,
  getWeight: (item, index) => {
    return item.weight;
  }
});

const array = [{fruit: 'pear', weight: 4}, {fruit: 'apple', weight: 30}];
customWeightedRandomIndex(array);
>>> 1


// If you intent to call the function multiple times on the same array,
// you should use the cached version instead:
import {createCachedWeightedRandomIndex} from 'pandemonium/weighted-random-index';

const array = [.1, .1, .4, .3, .1];
const customWeightedRandomIndex = createCachedWeightedRandomIndex(rng, array);

customWeightedRandomIndex();
>>> 3