bloom-filters/test/hyperloglog-test.js

JS implementation of probabilistic data structures: Bloom Filter (and its derived), HyperLogLog, Count-Min Sketch, Top-K and MinHash

/* file : hyperloglog-test.js
MIT License

Copyright (c) 2017-2020 Thomas Minier & Arnaud Grall

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

require('chai').should()
const {HyperLogLog} = require('../dist/api.js')

describe('HyperLogLog', () => {
  describe('#update', () => {
    it('should support update and cardinality estimations (count) operations', () => {
      const m = 2 ** 8
      const n = 10e4
      const sketch = new HyperLogLog(m)
      // populate the sketch with some values
      for (let i = 0; i < n; i++) {
        sketch.update(i.toString())
      }

      // Citation:
      // "Let σ ≈ 1.04/√m represent the standard error; the estimates provided by HYPERLOGLOG
      // are expected to be within σ, 2σ, 3σ of the exact count in respectively 65%, 95%, 99% of all
      // the cases"
      const exact_count = sketch.count()
      const relative_error = sketch.accuracy()

      let error
      const relative_errors = [
        relative_error,
        2 * relative_error,
        3 * relative_error,
      ]

      for (const relative_err of relative_errors) {
        try {
          Math.abs(n - exact_count).should.be.below(n * relative_err)
          error = false
          break
        } catch (e) {
          error = e
        }
      }

      if (error) {
        throw new Error(
          `should be withing σ, 2σ or 3σ: ${relative_errors
            .map(e => e * n)
            .toString()}: ${error.toString()}`
        )
      }
    }).timeout(0)
  })

  describe('#merge', () => {
    it('should peforms the union of two HyperLogLog sketches', () => {
      const first = new HyperLogLog(8)
      const second = new HyperLogLog(8)
      first.update('alice')
      first.update('bob')
      second.update('carol')
      second.update('daniel')

      const merged = first.merge(second)
      merged.nbRegisters.should.equals(first.nbRegisters)
      for (let i = 0; i < merged.nbRegisters; i++) {
        merged._registers[i].should.equal(
          Math.max(first._registers[i], second._registers[i])
        )
      }
    })

    it('should reject the union of two sketches with different number of registers', done => {
      const first = new HyperLogLog(8)
      const second = new HyperLogLog(32)
      try {
        first.merge(second)
        done(
          new Error(
            'The two sketches cannot be merged, as they have different number of registers'
          )
        )
      } catch (error) {
        done()
      }
    })
  })

  describe('#equals', () => {
    it('should returns True when two HyperLogLog sketches are equals', () => {
      const first = new HyperLogLog(8)
      const second = new HyperLogLog(8)
      first.update('alice')
      first.update('bob')
      second.update('alice')
      second.update('bob')
      first.equals(second).should.equal(true)
    })

    it('should returns False when two sketches have different number of registers', () => {
      const first = new HyperLogLog(8)
      const second = new HyperLogLog(16)
      first.equals(second).should.equal(false)
    })

    it('should returns False when two sketches have different content in their registers', () => {
      const first = new HyperLogLog(8)
      const second = new HyperLogLog(16)
      first.update('alice')
      first.update('bob')
      second.update('carol')
      second.update('daniel')
      first.equals(second).should.equal(false)
    })
  })

  describe('#saveAsJSON', () => {
    const sketch = new HyperLogLog(8)
    sketch.update('alice')
    sketch.update('bob')

    it('should export an HyperLogLog to a JSON object', () => {
      const exported = sketch.saveAsJSON()
      exported.type.should.equal('HyperLogLog')
      exported._nbRegisters.should.equal(sketch._nbRegisters)
      exported._nbBytesPerHash.should.equal(sketch._nbBytesPerHash)
      exported._correctionBias.should.equal(sketch._correctionBias)
      exported._registers.should.deep.equal(sketch._registers)
    })

    it('should create an HyperLogLog from a JSON export', () => {
      const exported = sketch.saveAsJSON()
      const newFilter = HyperLogLog.fromJSON(exported)
      newFilter.seed.should.equal(sketch.seed)
      newFilter._nbRegisters.should.equal(sketch._nbRegisters)
      newFilter._nbBytesPerHash.should.equal(sketch._nbBytesPerHash)
      newFilter._correctionBias.should.equal(sketch._correctionBias)
      newFilter._registers.should.deep.equal(sketch._registers)
    })

    it('should reject imports from invalid JSON objects', () => {
      const invalids = [
        {type: 'something'},
        {type: 'HyperLogLog'},
        {type: 'HyperLogLog', _nbRegisters: 1},
        {type: 'HyperLogLog', _nbRegisters: 1, _nbBytesPerHash: 1},
        {
          type: 'HyperLogLog',
          _nbRegisters: 1,
          _nbBytesPerHash: 1,
          _correctionBias: 2,
        },
      ]

      invalids.forEach(json => {
        ;(() => HyperLogLog.fromJSON(json)).should.throw(Error)
      })
    })
  })
})