Delete all equal items from array

Question

I have the next situation in my react application:
I have a state:

const [arr1, setArr1] = useState([1, 2, 3, 5, 1, 3]);

Bellow i render all items from array on UI like:

arr1.map(i => <li>{i}</li>)

Now i want to remove all items that are equal in the array:
ex:

1. [1, 2, 3, 5, 1, 3] // should be deleted 1 and 3 result: [1, 2, 5]
   
2. [1, 2, 3, 5, 3] // should be deleted 3 result: [1, 2, 5]
   Deleting all items also the state should change here arr1.map().
   I tried setArr1([new Set(arr1)]), but it does not delete all duplicated values, it delete just one of them.
   How to achieve what i described above?

Answer 1

You can count the frequency of number and then just pick the number whose frequency is 1.

const arr = [1, 2, 3, 5, 1, 3],
      frequency = arr.reduce((o,v) => (o[v] = (o[v] || 0) + 1, o), {}),
      unique = Object.keys(frequency).reduce((r,k) => frequency[k] === 1? [...r, +k]: r, []);
console.log(unique);

Answer 2

You can calculate the frequency and remove the number if the frequency is greater than 1. codesandbox

    function removeDuplicates(arr) {
    const frequency = {};
    arr.forEach((el) => {
      frequency[el] = frequency[el] ? ++frequency[el] : 1;
    });

    const result = [];
    for (el in frequency) {
      if (frequency[el] === 1) {
        result.push(el);
      }
    }

    return result;
 }
  

    const arrayWithoutDuplicates = removeDuplicates(arr1);
      return (
        <ul>
          {arrayWithoutDuplicates.map((el) => {
            return <li key={el}> {el} </li>;
          })}
        </ul>
      );

Answer 3

Check if the the first index equal to the last index on an element,when they are equals it means it is unique:

let result = []
let arr = [1, 2, 3, 5, 1, 3]

arr.forEach(e => arr.indexOf(e) === arr.lastIndexOf(e)?result.push(e):null)

console.log(result)

Answer 4

Below is a one-liner using filter

const arr = [1, 2, 3, 5, 1, 3];

const unique = arr.filter(x => arr.filter(y => y === x).length < 2)
console.log(unique);