How to filter only 1 matching element in array

Question

I have 2 apples in array. Filter method deletes all apples. Is there a way to delete only 1 of them.

var box = ['banana', 'apple', 'apple']

Output that I'm expectig:

box.filter((a) => a !== 'apple') => ['banana', 'apple']

Are you asking for a function that deletes duplicates? Did you search? There are many Q&A about that already.... — trincot, Mar 20 '21 at 10:57
@trincot - I don't read it that way, but I can see how someone would. Taner - What result would you expect on `["banana", "apple", "pear", "apple", "orange", "apple"]`? — T.J. Crowder, Mar 20 '21 at 11:00
If there are three `"apples"` in the array should it still only return one? — pilchard, Mar 20 '21 at 11:08
The question means that `only one element should be removed`. I do not know why the question was closed. I am waiting for @Taner for explanation. — wittgenstein, Mar 20 '21 at 11:10
That isn't clear @wittgenstein. In the example case removing one also has the effect of making it unique. — pilchard, Mar 20 '21 at 11:11
@ Taner - Stack Overflow is a **very** active place, even on the weekend. When you post a question (or an answer), *stick around* for a few minutes so you can respond to anything that comes up in the comments. — T.J. Crowder, Mar 20 '21 at 11:27

score 3 · Accepted Answer · answered Mar 20 '21 at 10:58

Nothing built-in, no. You can remember whether you've seen it and always return true afterward:

const box = ["banana", "apple", "apple"];

let seenApple = false;
const filtered = box.filter((a) => {
    if (seenApple) {
        return true;
    }
    seenApple = a === "apple";
    return !seenApple;
});

console.log(filtered);

Alternatively you could find the index of the first apple:

const appleIndex = box.findIndex(a => a === "apple");

...and then either filter by that index:

const filtered = box.filter((entry, index) => index !== appleIndex);

...or use splice to modify the array in-place.

score 1 · Answer 2 · answered Mar 20 '21 at 10:57

1

Are you looking to remove duplicates? If you just want an array with unique elements, you can do something like this

var unique_arr = arr.filter(function(elem, index, self) {
    return index === self.indexOf(elem);
})

answered Mar 20 '21 at 10:57

Niraeth

315
2
4

1

*"...to delete only 1 of them..."* doesn't sound like "remove duplicates" to me. But if so, yes, this is good enough for a small array. Lots of repeated searching, though, so scales not very well. – T.J. Crowder Mar 20 '21 at 10:58
This is blowing my mind right now. – T_lastname Sep 21 '22 at 07:37

score 0 · Answer 3 · answered Mar 20 '21 at 10:59

You could take a closure with another variable for overriding the condition.

const
    box = ['banana', 'apple', 'apple'],
    result = box.filter(
        (found => a => a !== 'apple' || found || !(found = true))
        (false)
    );

console.log(result);

How to filter only 1 matching element in array

3 Answers3