tests.js

var HyperLogLog = require('./hyperloglog')
var hash = HyperLogLog.hash
var vows = require('vows')
var assert = require('assert')

vows.describe('HyperLogLog').addBatch({
  'empty hll has cardinality of zero': function () {
    assert.equal(HyperLogLog(8).count(), 0)
  },

  'counts unique things': function () {
    var thing1 = hash('thing1')
    var thing2 = hash('thing2')
    var thing3 = hash('thing3')

    var hll = HyperLogLog(8)

    hll.add(thing1)

    assert.equal(hll.count(), 1)

    for (var i = 0; i < 100; ++i) {
      hll.add(thing1)
      hll.add(thing2)
      hll.add(thing3)
    }

    assert.equal(hll.count(), 3)
  },

  'counts large set of unique values': function () {
    const valueSetSize = 1000
    const randomSeed = 8383838383
    const randomValueArray = Array.from({ length: valueSetSize }, () => Math.floor(Math.random() * randomSeed))
    const randomValueSet = Array.from(new Set(randomValueArray))

    var hll = HyperLogLog(12)
    randomValueSet.forEach(value => hll.add(hash(value.toString())))

    const smoothedRelativeError = Math.ceil(hll.relative_error() * 100) / 100
    const errorMargin = smoothedRelativeError * valueSetSize
    const minAcceptable = Math.floor(valueSetSize - errorMargin)
    const maxAcceptable = Math.ceil(valueSetSize + errorMargin)
    const got = hll.count()
    console.log(`max ${maxAcceptable} | min ${minAcceptable} - got ${hll.count()}`)
    assert.equal(hll.count() <= maxAcceptable && hll.count() >= minAcceptable, true)

  },

  'merges overlapping counts': function () {
    var hll = HyperLogLog(15)
    var hll2 = HyperLogLog(15)

    for (var i = 0; i < 100; ++i) {
      hll.add(hash('Just hll ' + i))
      hll2.add(hash('Just hll2 ' + i))
      var both = hash('Both ' + i)
      hll.add(both)
      hll2.add(both)
    }

    assert(Math.abs(hll.count() - 200) <= 2)
    assert(Math.abs(hll2.count() - 200) <= 2)

    hll.merge(hll2.output())

    assert(Math.abs(hll.count() - 300) <= 3)
  },

  'merges bigger HLL into a smaller one': function () {
    var hll = HyperLogLog(8)
    var hll2 = HyperLogLog(14)

    var original_relative_error = hll.relative_error()

    hll.add(hash('Just hll'))
    hll2.add(hash('Just hll2'))
    var both = hash('both')
    hll.add(both)
    hll2.add(both)

    hll.merge(hll2.output())

    assert.equal(hll.count(), 3)
    assert(hll.relative_error() == original_relative_error)
  },

  'merges a smaller HLL into a bigger one': function () {
    // The result is the same size as the smaller one.
    var hll = HyperLogLog(14)
    var hll2 = HyperLogLog(8)

    var original_relative_error = hll.relative_error()

    hll.add(hash('Just hll'))
    hll2.add(hash('Just hll2'))
    var both = hash('both')
    hll.add(both)
    hll2.add(both)

    hll.merge(hll2.output())

    assert.equal(hll.count(), 3)
    assert(hll.relative_error() > original_relative_error)
  }
}).export(module)