redux-ab-test/src/utils/random-variation.js

A/B testing React components with Redux and debug tools. Isomorphic with a simple, universal interface. Well documented and lightweight. Tested in popular browsers and Node.js. Includes helpers for React, Redux, and Segment.io

/** @flow */
import Immutable  from 'immutable';
import { logger } from './logger';

// Helper to convert variation => weight:number
export const toWeight = (variation:Immutable.Map) => { return variation.get('weight') || 0; };

// Calculate the total weight
export const toTotal = (variations:Immutable.List) => variations.reduce( (total:number, variation:Immutable.Map) => { return total + toWeight(variation); }, 0);

// Generate the next range in the series
export const toRange = (list:Immutable.List, counter:number) => {
  const startAt = list.count() <= 0 ? 0 : (list.last().last() + 1);
  const range = Immutable.Range(startAt, startAt + counter);
  return list.push(range);
};

// Geneate a contigious range of scores
export const toRanges = (variations:Immutable.List) => variations.map(toWeight).reduce(toRange, Immutable.List([]));

export default function randomVariation(experiment:Immutable.Map, random:Function = Math.random) {
  const variations = experiment.get('variations').sortBy(toWeight).reverse();
  const weightTotal = toTotal(variations);
  const weightRanges = toRanges(variations);
  const weightRandom = Math.round(weightTotal * random());
  logger(`${__filename} randomVariation experiment.name='${experiment.get('name')}', variations='${JSON.stringify(variations)}'`);
  logger(`${__filename} randomVariation experiment.name='${experiment.get('name')}', weightTotal='${JSON.stringify(weightTotal)}'`);
  logger(`${__filename} randomVariation experiment.name='${experiment.get('name')}', weightRanges='${JSON.stringify(weightRanges)}'`);
  logger(`${__filename} randomVariation experiment.name='${experiment.get('name')}', weightRandom='${JSON.stringify(weightRandom)}'`);

  // Find the range that contains our score
  const index = weightRanges.findIndex(range => range.includes(weightRandom));
  logger(`${__filename} randomVariation experiment.name='${experiment.get('name')}', index='${JSON.stringify(index)}'`);

  // Return the matching variation.  Returns variations.last() if random() was out of range [0, 1)
  const variation = variations.get(index, variations.last());
  logger(`${__filename} randomVariation experiment.name='${experiment.get('name')}', variation.name='${variation && variation.get('name')}'`);
  return variation;
}