Math

_randomInt

Returns a random integer in the provided range. As usual, lower-bound is inclusing, while higher-bound is exclusive. Unusually, both lower and higher bounds are inclusive.

_randomInt(1, 3)
// 1
// 3
// 2

_randomArrayItem

Returns a random item from the given array.

Don't use it on empty array. It'll return undefined in that case, but that is not reflected in function's output type!

const a = [1, 2, 3]
_randomArrayItem(a)
// random of 1, 2 or 3

_createDeterministicRandom

Returns a "deterministic Math.random() function".

Useful to make tests that need to use Math.random() deterministic.

const deterministicRandom = _createDeterministicRandom()

deterministicRandom()
// => 0.9872818551957607

deterministicRandom()
// => 0.34880331158638

Based on this gist which is based on Robert Jenkins’ 32 bit integer hash function.

_average

Calculate an average of the array of numbers.

_average([1, 2, 3, 4])
// 2.5

_averageWeighted

Calculate a "weighted average", given the array of numbers and corresponding array of weights.

const numbers = [1, 2]
const weights = [3, 1]
_averageWeighted(numbers, weights)
// 1.25

_median

Calculate a Median of the array of numbers.

_median([1, 2, 3]) // 2
_median([1, 2, 3, 4]) // 2.5
_median([1, 1, 1, 3, 999]) // 1

_percentile

Calculate a Percentile of the array of numbers.

const numbers = [1200, 1400]
_percentile(numbers, 0) // 1200
_percentile(numbers, 10) // 1220
_percentile(numbers, 20) // 1240
_percentile(numbers, 30) // 1260
_percentile(numbers, 40) // 1280
_percentile(numbers, 50) // 1300
_percentile(numbers, 60) // 1320
_percentile(numbers, 70) // 1340
_percentile(numbers, 80) // 1360
_percentile(numbers, 90) // 1380
_percentile(numbers, 100) // 1400

SimpleMovingAverage

// SMA with the size of 2:
const sma = new SimpleMovingAverage(2)
sma.avg // 0 by default, when no numbers were pushed

sma.push(1) // [1]
sma.avg // 1

sma.push(2) // [1, 2]
sma.avg // 1.5

sma.push(3) // [1, 2, 3]
sma.avg // 2.5