ttest/hypothesis.js

Perform the Student's t hypothesis test

'use strict';

const OneDataSet = require('./hypothesis/one-data-set.js');
const TwoDataSet = require('./hypothesis/two-data-set.js');
const Welch = require('./hypothesis/welch.js');

const Summary = require('summary');

const ALTERNATIVE_MAP = Object.assign(Object.create(null), {
  'not equal': 0,
  'less': -1,
  'greater': 1
});

function isSummary(data) {
  return data && (typeof data.mean === 'function' &&
                  typeof data.variance === 'function' &&
                  typeof data.size === 'function');
}

function isCalculated(data) {
  return data && (typeof data.mean === 'number' &&
                  typeof data.variance === 'number' &&
                  typeof data.size === 'number');
}

function isCompatible(structure) {
  return Array.isArray(structure) ||
         isSummary(structure) ||
         isCalculated(structure);
}

function toData(data) {
  if (Array.isArray(data) || isSummary(data)) {
    const summary = isSummary(data) ? data : new Summary(data);
    return {
      mean: summary.mean(),
      variance: summary.variance(),
      size: summary.size()
    };
  } else {
    return data;
  }
}

function hypothesis(left, right, options) {
  // Vertify required arguments
  if (!isCompatible(left)) {
    throw new TypeError(
      'left value in hypothesis test must be an array or data summary'
    );
  }

  if (!isCompatible(right)) {
    options = right;
    right = undefined;
  }

  // Set the default options
  options = Object.assign({
    mu: 0,
    varEqual: false,
    alpha: 0.05,
    alternative: 'not equal'
  }, options);

  // Convert alternative value
  options.alternative = ALTERNATIVE_MAP[options.alternative];

  // Vertify mu option
  if (typeof options.mu !== 'number') {
    throw new TypeError('mu option must be a number');
  }

  // Vertify varEqual option
  if (typeof options.varEqual !== 'boolean') {
    throw new TypeError('varEqual option must be a boolean');
  }

  // Vertify alpha option
  if (typeof options.alpha !== 'number') {
    throw new TypeError('alpha option must be a number');
  }
  if (options.alpha >= 1) {
    throw new RangeError('alpha must be below 1.0');
  }

  // Vertify alternative option
  if (typeof options.alternative === 'undefined') {
    throw new Error('alternative must be either "not equal", "less" or "greater"');
  }

  // Perform the student's t test
  if (isCompatible(right)) {
    if (options.varEqual) {
      return new TwoDataSet(toData(left), toData(right), options);
    } else {
      return new Welch(toData(left), toData(right), options);
    }
  } else {
    return new OneDataSet(toData(left), options);
  }
}
module.exports = hypothesis;