Finding Occurences of element in array in js

Hello guys today i want to show you how to find number of occurence of element in an array in javascript and also their index.

Lets get started...

Code -

let array = [6,1,4,4,2,8,3,4,4,4,5,10,5,9,11,
6,1,4,4,2,8,3,4,4,4,5,10,5,9,11,6,1,4,4,2,8,3,4,4,4,5,10,5,9,11];
let target = 4

const occurences = (array,target) => {
  let result = 0
  let index = []
  for (let i = 1; i <= array.length + 1; i++) {
    if(array[i] === target){
     result++
     index.push(i)
    }
    else{
      continue
    }
  }
  return `${target} occured ${result.length} times at indexes - ${index}`
}

console.log(occurences(array,target))

Output -

4 occured 15 times at indexes - 2,3,7,8,9,17,18,22,23,24,32,33,37,38,39

• So first we have created an arrow function with two parameter namely array and target.Array will be the one which we are going to perform our searching for occurences and target is the element we want to find how many times it occured in the array and which index.
• We created two variable result and index.Result will hold the target occurence number and index will hold the indexes of that occurence in the array.
• We created a for loop which will iterate through the array to last element.
• Then we have created a condition with "if" as if the element at current index element is equal to the target element then increase the result with 1 and push the index of that element to the index array and if the element at current index is not equal to the target element then continue the iteration to the next element using "continue" keyword.
• In the end we have return the statement using string interpolation with number of occurences and their indexes.

Thats it for this post.
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Also check these posts as well
https://dev.to/shubhamtiwari909/javascript-map-with-filter-2jgo

https://dev.to/shubhamtiwari909/e-quotes-3bng

https://dev.to/shubhamtiwari909/deploy-react-app-on-netlify-kl

Comments

[𒎏Wii 🏳️‍⚧️]

array = [6,1,4,4,2,8,3,4,4,4,5,10,5,9,11,
6,1,4,4,2,8,3,4,4,4,5,10,5,9,11,6,1,4,4,2,8,3,4,4,4,5,10,5,9,11];
array
   .map((val, index) => val==4 ? index : undefined)
   .filter(value=>value!=undefined)

By the way, that else { continue } at the end of the loop is completely useless.

[Shubham Tiwari]

This is also a better approach thank you

[Jon Randy 🎖️]

Your code returns (if we fix the spelling mistake):

"4 occurred undefined times at indexes - 2,3,7,8,9,17,18,22,23,24,32,33,37,38,39"

Also, the else clause in your code is entirely redundant, and the target will not be found if it appears at index 0.

Overall, this problem would seem a good use case for reduce:

const occurrences = (array,target) => {
  const result = array.reduce(
    (indexes, value, index) => (value===target && indexes.push(index), indexes), []
  )
  return `${target} occurred ${result.length} times at indexes - ${result}`
}

[Shubham Tiwari]

Can you please write the whole code with if statement

[Jon Randy 🎖️]

Like this?

const occurrences = (array, target) => {
  const result = array.reduce(
    (indexes, value, index) => {
      if (value===target) indexes.push(index)
      return indexes
    }, []
  )
  return `${target} occurred ${result.length} times at indexes - ${result}`
}

[Shubham Tiwari]

Yeah thank you sir
I also want to know is there any performance or any type of difference in my way of implementing and your way of implementing or its just about cleaner way of writing this ?

[Jon Randy 🎖️]

A quick check on Chrome shows that the reduce method is around 70% faster

[Shubham Tiwari]

Okayss