JavaScript transforming an array into a counter

Question

JavaScript transforming an array into a counter

I am seeking a way to transform a one-dimensional array into a frequency dictionary in JavaScript. The array elements should serve as keys, while their frequencies act as values.

Take, for example, the Python script below, which generate a list of 1024 random numbers ranging from 0 to 255, and then count their occurrences:

import random
from collections import Counter

sorted(Counter(random.randbytes(1024)).items(), key=lambda x: -x[1])

I can achieve the same in JavaScript, albeit not as succinctly:

var numbers = Array.from({length: 1024}, () => Math.floor(Math.random() * 256))
var counter = Object()

for (let number of numbers) {
    if (counter.hasOwnProperty(number)) {counter[number] += 1}
    else {counter[number] = 1}
}

Object.entries(counter).sort(([,a],[,b]) => b-a)

Is there an easier way to accomplish this task more concisely?

javascript arrays

Answer 1

Answer №1

This particular test result caught me off guard: when running tests with 100 million numbers on my Mac, the Map version took 2.7s, whereas the Object version only took 0.6s.

(Interestingly, the original version performs the same as the Object version in the code snippet below)

const numbers = Array.from({length:10**8},()=>Math.random()*256|0)

let timerStart = new Date()
{
  let counter = new Map()
  numbers.forEach(n=>counter.set(n,(counter.get(n)??0)+1))
  counter = new Map([...counter].sort(([,a],[,b]) => b-a))
}

console.log(`Map version took ${new Date()-timerStart} ms`)

timerStart = new Date()
{
  let counter = numbers.reduce((a,c)=>(a[c]=(a[c]??0)+1,a),{})
  Object.entries(counter).sort(([,a],[,b]) => b-a)
}

console.log(`Object version took ${new Date()-timerStart} ms`)

Answer 2

This particular test result caught me off guard: when running tests with 100 million numbers on my Mac, the Map version took 2.7s, whereas the Object version only took 0.6s.

(Interestingly, the original version performs the same as the Object version in the code snippet below)

const numbers = Array.from({length:10**8},()=>Math.random()*256|0)

let timerStart = new Date()
{
  let counter = new Map()
  numbers.forEach(n=>counter.set(n,(counter.get(n)??0)+1))
  counter = new Map([...counter].sort(([,a],[,b]) => b-a))
}

console.log(`Map version took ${new Date()-timerStart} ms`)

timerStart = new Date()
{
  let counter = numbers.reduce((a,c)=>(a[c]=(a[c]??0)+1,a),{})
  Object.entries(counter).sort(([,a],[,b]) => b-a)
}

console.log(`Object version took ${new Date()-timerStart} ms`)

Answer 3

Answer №2

Check out this efficient ES6 solution using Array.reduce and the comma operator for a one-liner code snippet:

const numbers = Array.from({length: 1024}, () => Math.floor(Math.random() * 256))

const counter = numbers.reduce((acc, num) => (acc[num] = (acc[num] || 0) + 1, acc), {})

const sorted = Object.entries(counter).sort(([,a],[,b]) => b-a)

console.log(sorted)

Answer 4

Check out this efficient ES6 solution using Array.reduce and the comma operator for a one-liner code snippet:

const numbers = Array.from({length: 1024}, () => Math.floor(Math.random() * 256))

const counter = numbers.reduce((acc, num) => (acc[num] = (acc[num] || 0) + 1, acc), {})

const sorted = Object.entries(counter).sort(([,a],[,b]) => b-a)

console.log(sorted)

Answer 5

Answer №3

If you're looking to implement a more efficient solution, consider utilizing a Map data structure:

const items = Array.from({length: 1000}, () => Math.floor(Math.random() * 200))

const mappedItems = items.reduce((accum, item) => accum.set(item, (accum.get(item) || 0) + 1), new Map());

Answer 6

If you're looking to implement a more efficient solution, consider utilizing a Map data structure:

const items = Array.from({length: 1000}, () => Math.floor(Math.random() * 200))

const mappedItems = items.reduce((accum, item) => accum.set(item, (accum.get(item) || 0) + 1), new Map());

Answer 7

Answer №4

An easy way to enhance the code's readability is by utilizing the ternary operator for a more concise expression.

const numbers = Array.from({length: 1024}, () => Math.floor(Math.random() * 256));
const counter = Object();

for (let number of numbers) {
    counter[number] = counter.hasOwnProperty(number) ? counter[number] + 1 : 1;
}

Object.entries(counter).sort(([,a],[,b]) => b-a);

Answer 8

An easy way to enhance the code's readability is by utilizing the ternary operator for a more concise expression.

const numbers = Array.from({length: 1024}, () => Math.floor(Math.random() * 256));
const counter = Object();

for (let number of numbers) {
    counter[number] = counter.hasOwnProperty(number) ? counter[number] + 1 : 1;
}

Object.entries(counter).sort(([,a],[,b]) => b-a);

JavaScript transforming an array into a counter

Answer №1

Answer №2

Answer №3

Answer №4

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