Cannot filter only unique values of an array

Question

I'm trying to write a function that accepts an array of objects, selects only a specific key in the objects and returns only the unique values of that array into a new "filtered" array. I'm trying to use Array.filter and keep getting errors that my filtered array is undefined. Where have I gone wrong?

const findUniques = function(arr) {


let rawArray = arr.map(res => res.id);

let filtered = rawArray.filter((id) => {
    return filtered.indexOf(id) === -1;
});
console.log(filtered)


};

Here is a mock of the array I'm filtered over.

1630489261, 1630489261, 1630489261, 1630489313, 1630489313, 1630489261, 1630489313, 1707502836, 1590711681, 1588295455, 1630489313, 1707502836, 1588295455, 1707502836, 1590711681, 1707502836, 1707502836, 1707502836, 1707502836, 1707502836, 1588295455, 1588295455

If I set filtered as a global variable it gets filled but it is not being filtered. I.E. filtered is being filled with everything in the rawArray.

please provide to us at least the mock of your response(res var) — Yuri Pereira, Jul 02 '17 at 15:09
I think your code should lead to some initialization errors since for example you are using "filtered" variable before it is initialized. — jrook, Jul 02 '17 at 15:17
Did you read this : https://stackoverflow.com/questions/9229645/remove-duplicates-from-javascript-array — Mohamed Abbas, Jul 02 '17 at 15:17
Also, since you are reporting you are getting *undefined* errors, it may be because you are declaring your function as *const*. See [here](https://stackoverflow.com/questions/33040703/proper-use-of-const-for-defining-functions-in-javascript) — jrook, Jul 02 '17 at 15:25
@Somethingismissing Check my updated answer https://stackoverflow.com/a/44872354/6568620 — Mohamed Abbas, Jul 02 '17 at 16:01

Mohamed Abbas · Accepted Answer · 2017-07-02T16:00:01.867

0

Using Array#filter

rawArray = [1, 2, 3, 2, 3, 1, 4];

filtered = rawArray.filter((e, i) => rawArray.indexOf(e) === i);
    
console.log(filtered);

Using Array#reduce

let rawArray = [1, 2, 3, 2, 3, 1, 4],
filtered = rawArray.reduce(function (acc, item) {
    if (!acc.includes(item)){
        acc.push(item);
    }
    return acc; 
}, []);
console.log(filtered);

edited Jul 02 '17 at 16:00

answered Jul 02 '17 at 15:20

Mohamed Abbas

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Could you explain how the implicit return of the Array.filter option is working. How does rawArray.indexOf(e) === i) returning true or false – Jul 02 '17 at 21:53
@Somethingismissing `rawArray.indexOf(e) === i` to check if this item added before or not, this fiddle will help to understand what happens inside filter (filter in our case) https://jsfiddle.net/ee5s067q/ – Mohamed Abbas Jul 02 '17 at 22:15
@Somethingismissing As filter works like the loop `e` represent the current element in the original array (rawArray). `i` represented the current index of the new array (filtered) – Mohamed Abbas Jul 02 '17 at 22:16

score 0 · Answer 2 · answered Jul 02 '17 at 15:22

const values = [1630489261, 1630489261, 1630489261, 1630489313, 1630489313, 1630489261, 1630489313, 1707502836, 1590711681, 1588295455, 1630489313, 1707502836, 1588295455, 1707502836, 1590711681, 1707502836, 1707502836, 1707502836, 1707502836, 1707502836, 1588295455, 1588295455];


function unique(array) {
  return array.reduce((a,b) => {
    let isIn = a.find(element => {
        return element === b;
    });
    if(!isIn){
      a.push(b);
    }
    return a;
  },[]);
}

let ret = unique(values);

console.log(ret);

https://jsfiddle.net/26bwknzf/4/

You don't need to use `find` that require a function. you can simply use `indexOf` or `includes`. — Mohamed Abbas, Jul 02 '17 at 15:24

Cannot filter only unique values of an array

2 Answers2