Deleting both values from array if duplicate - JavaScript/jQuery

user_1144247 0
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I have an array here:

var myArr = [1, 1, 2, 5, 5, 7, 8, 9, 9];

Now I want to remove both appearances of a duplicate. So the desired result is not:

var myArr = [1, 2, 5, 7, 8 ,9];

but

var myArr = [2, 7, 8];

Basically I know how to remove duplicates, but not in that that special way. Thats why any help would be really appreciated!

Please note: My array is filled with strings. The numbers here were only used as an example.

arrays jquery javascript
9 Answers

Using Hashmap

  1. create hashmap and count occurencies
  2. filter where hashmap.get(value) === 1 (only unique values)
const myArray = [1, 1, 2, 5, 5, 7, 8, 9, 9];
const map = new Map();
myArray.forEach(v => map.set(v, map.has(v) ? map.get(v)+1 : 1));
myArray.filter(v => map.get(v) === 1);

Old version (slower but valid too)

Heres a short version using Array.filter(). The trick is to first find all values that are NOT uniqe, and then use this array to reject all unique items in the original array.

let myArr = [1, 1, 2, 5, 5, 7, 8, 9, 9];
let duplicateValues = myArr.filter((item, indx, s) => s.indexOf(item) !== indx);
myArr.filter(item => !duplicateValues.includes(item));
// => [2, 7, 8]
user_62720610

You can use Set (available in IE 11+) as below

const sourceArray = [1, 2, 3, 4, 5, 5, 6, 6, 7, 7, 8];
const duplicatesRemoved = new Set();

sourceArray.forEach(element => {
    if (duplicatesRemoved.has(element)) {
        duplicatesRemoved.delete(element)
    } else {
        duplicatesRemoved.add(element)
    }
})

console.log(Array.from(duplicatesRemoved))

N.B. Arrow functions are not supported in older browsers. Use normal function syntax for that instead. However, Array.from can easily be polyfilled for older browsers.

Try it here.

user_24597890
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