Outliers: z-score and modified z-score method in JavaScript

modified-z-score.js

// z-score
const { mean, deviation } = require('d3-array')

const zscore = input => {
	const arrMean = mean(input)
	// here the n-1 : http://duramecho.com/Misc/WhyMinusOneInSd.html
	const arrDeviation = deviation(input)
	return input.map(i => ({
		zscore: (i - arrMean) / arrDeviation,
		item: i,
	}))
}

const findOutliersZ = input => {
  return zscore(input).filter(x => x.zscore >= 3 || x.zscore <= -3).map(x => x.item)
}

/** MODIFIED ZSCORE ***/
const R = require('ramda')
const zscorem = input => {
	// const arrMean = mean(input)
	// here the n-1 : http://duramecho.com/Misc/WhyMinusOneInSd.html
	// const arrDeviation = deviation(input)

	const medianY = R.median(input)
	medianY //?
	// MAD
	const medianAbsDeviationY = R.median(
		input.map(y => Math.abs(y - medianY))
	)
	medianAbsDeviationY //?

	
	const MODIFIED_Z_SCORE_CONST = 0.6745
	return input.map(y => ({
		zscore: MODIFIED_Z_SCORE_CONST * (y - medianY) / medianAbsDeviationY,
		item: y,
	}))
}

const findOutliersZ = input => {
  return zscorem(input).filter(x => x.zscore >= 3.5 || x.zscore <= -3.5).map(x => x.item)
}