Removing duplicate array values and then storing them [react]

Question

I'm trying to strip the duplicate array values from my current array. And I'd like to store the fresh list (list without duplicates) into a new variable.

var names = ["Daniel","Lucas","Gwen","Henry","Jasper","Lucas","Daniel"];

const uniqueNames = [];
const namesArr = names.filter((val, id) => {
    names.indexOf(val) == id;  // this just returns true
});

How can I remove the duplicated names and place the non-duplicates into a new variable?

ie: uniqueNames would return...

["Daniel","Lucas","Gwen","Henry","Jasper"]

(I'm using react jsx) Thank you!

Somebody upvoted my original answer, which I deleted because I didn't fully understand the question (and it was probably wrong anyway). The meat of it was that you're missing a `return` inside your filter! — Scott, May 13 '16 at 19:35
@WildWidow I wasn't sure if he wanted the array to contain the removed elements, or the array after those elements were removed. — Scott, May 13 '16 at 19:41
@ScottKaye the array after the duplicates were removed :) sorry should have specified — Modelesq, May 13 '16 at 19:42
@ScottKaye when I was typing my solution, I think I glimpsed at your solution just before I submit mine, I believe you had the answer for bot h removed elements and the existing elements which is correct :) — Wild Widow, May 13 '16 at 19:43

Lewix · Accepted Answer · 2016-05-13T21:00:49.157

You can do it in a one-liner

const uniqueNames = Array.from(new Set(names));

// it will return a collection of unique items

Note that @Wild Widow pointed out one of your mistake - you did not use the return statement. (it sucks when we forget, but it happens!)

I will add to that that you code could be simplified and the callback could be more reusable if you take into account the third argument of the filter(a,b,c) function - where c is the array being traversed. With that said you could refactor your code as follow:

const uniqueNames = names.filter((val, id, array) => {
   return array.indexOf(val) == id;  
});

Also, you won't even need a return statement if you use es6

const uniqueNames = names.filter((val,id,array) => array.indexOf(val) == id);

Infaz · Answer 2 · 2022-06-09T18:17:11.277

If you want to remove duplicate values which contains same "id", You can use this.

const arr = [
  { id: 2, name: "sumit" },
  { id: 1, name: "amit" },
  { id: 3, name: "rahul" },
  { id: 4, name: "jay" },
  { id: 2, name: "ra one" },
  { id: 3, name: "alex" },
  { id: 1, name: "devid" },
  { id: 7, name: "sam" },
  ];

function getUnique(arr, index) {

  const unique = arr
       .map(e => e[index])

       // store the keys of the unique objects
       .map((e, i, final) => final.indexOf(e) === i && i)
  
       // eliminate the dead keys & store unique objects
      .filter(e => arr[e]).map(e => arr[e]);      

   return unique;
}

console.log(getUnique(arr,'id'))

Result :

[ 
  { id: 2, name: "sumit" },
  { id: 1, name: "amit" },
  { id: 3, name: "rahul" },  
  { id: 4, name: "jay" },  
  { id: 7, name: "sam" }
]

Since I found this code very confusing, I posted the refactored version as a separate answer. — Anly, Aug 24 '20 at 16:50

score 2 · Answer 3 · answered May 13 '16 at 19:35

2

you forgot to use return statement in the filter call

const namesArr = duplicatesArray.filter(function(elem, pos) {
    return duplicatesArray.indexOf(elem) == pos;
});

answered May 13 '16 at 19:35

Wild Widow

2,359
3
22
34

score 1 · Answer 4 · answered Aug 24 '20 at 16:48

Since I found the code of @Infaz 's answer used somewhere and it confused me greatly, I thought I would share the refactored function.

function getUnique(array, key) {
  if (typeof key !== 'function') {
    const property = key;
    key = function(item) { return item[property]; };
  }
  return Array.from(array.reduce(function(map, item) {
    const k = key(item);
    if (!map.has(k)) map.set(k, item);
    return map;
  }, new Map()).values());
}

// Example
const items = [
  { id: 2, name: "sumit" },
  { id: 1, name: "amit" },
  { id: 3, name: "rahul" },
  { id: 4, name: "jay" },
  { id: 2, name: "ra one" },
  { id: 3, name: "alex" },
  { id: 1, name: "devid" },
  { id: 7, name: "sam" },
];
console.log(getUnique(items, 'id'));
/*Output:
[ 
  { id: 2, name: "sumit" },
  { id: 1, name: "amit" },
  { id: 3, name: "rahul" },  
  { id: 4, name: "jay" },  
  { id: 7, name: "sam" }
]
*/

Finally, one answer worked. Thanks. – Lalit Fauzdar Sep 18 '21 at 17:13 — Lalit Fauzdar, Sep 18 '21 at 17:13

score 1 · Answer 5 · answered Jan 14 '21 at 09:45

1

Also you can do this

{Array.from(new Set(yourArray.map((j) => j.location))).map((location) => (
          <option value={`${location}`}>{location}</option>
        ))}

answered Jan 14 '21 at 09:45

VGabriel45

91
6

Removing duplicate array values and then storing them [react]

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