Code Snippet Series: Get Unique Values from Array
#javascript#performance#algorithms#beginners
Functional Javascript

Functional Javascript @functional_js

About: Full Stack System Designer and Software Engineer

Location:
Vancouver
Joined:
Jan 2, 2019

Code Snippet Series: Get Unique Values from Array

Publish Date: Aug 4 '20
5 4

Here are three ways to retrieve the unique set of primitive values from an array....

//a. Set-Array.from
const getUniq_ArrayFrom = a => Array.from(new Set(a));

//b. Set-Spread
const getUniq_Set = a => [...new Set(a)];

//c. good ol' Loop
const getUniq_Loop = a => {
  const o = {};
  for (let i = 0; i < a.length; i++) {
    o[a[i]] = true;
  }
  return Object.keys(o);
};


//@perfTests

timeInLoop("getUniq_ArrayFrom", 1, () => getUniq_ArrayFrom(aNums));
// getUniq_ArrayFrom: 1e+0: 513.777ms

timeInLoop("getUniq_Set", 1, () => getUniq_Set(aNums));
// getUniq_Set: 1e+0: 521.112ms

timeInLoop("getUniq_Loop", 1, () => getUniq_Loop(aNums));
// getUniq_Loop: 1e+0: 44.433ms

I think we have a clear winner here. 🏆
The loop wins by over 10X

Notes:

using an array of 10 million numbers between 1 and 100 (high duplication), the Loop idiom is 10X faster...

const aNums = genRandNums(1, 100, 1e7);

using an array of 10 million numbers between 1 and a million (low duplication), the Loop idiom is only 2X faster...

const aNums = genRandNums(1, 1e6, 1e7);

TimeInLoop Source Code:

https://gist.github.com/funfunction/91b5876a5f562e1e352aed0fcabc3858

Comments 4 total

  • Marcell Cruz
    Marcell CruzAug 4, 2020

    Interesting, why is Set so slow, I would have guessed that it was going to be a lot faster

  • Nicholas Fazzolari
    Nicholas FazzolariAug 4, 2020

    Thank you for sharing the timeInLoop source code. Is the console.time() function where the measurement of time is actually done. I wonder how runtime is calculated in the Console code module.

  • Pacharapol Withayasakpunt
    Pacharapol WithayasakpuntAug 4, 2020

    jsperf.com/unique-arrays-1

    Objects won't work with non-string keys, as well as nasty strings (e.g. __proto__).

    • Functional Javascript
      Functional JavascriptAug 4, 2020

      Correct, these funcs work with the primitives (string and number).

      Ref types (comparing objects and arrays) require custom logic, even if working with Set and Map.

      eg...

      const aDups = [{ id: 1 }, { id: 1 }, { id: 1 }, { id: 1}];
const setDups = new Set(aDups)
console.log(setDups)

// output:
// Set(4) { { id: 1 }, { id: 1 }, { id: 1 }, { id: 1 } }
Add comment