CODEWITHSUNDEEP
javascript
Apostolos
Apostolos

Reputation: 598

filter an array with same elements

I am trying to filter an array with the same elements by using the indexOf function. But it fails and I do not understand why. To be more clear I want to filter by giving the position of an element, but it fails in array with two same elements. Could you please help ?

words = ['One', 'Two', 'myWord', 'Three', 'myWord', 'Four'];
    
words = words.filter(item => words.indexOf(item) != 2);
console.log(words);
// expected output: Array ['One', 'Two', 'Three', 'myWord', 'Four'],
// the first myWord in position 2 is excluded but not the one in position 4

Upvotes: 0

Views: 1091

Answers (4)

fedeghe
fedeghe

Reputation: 1317

if What You need is really filter for a specific position then

const index = 2
words = words.filter((item, i) => i != index);

but it does not perform so well since has to loop over all the elements, I would opt for something like the following:

words = [...words.slice(0, index), ...words.slice(index+1)]

they behave the same as long as index >= 0 so a wrapping function would be a good thing.

There is any particular reason why You want to use indexOf ?

Upvotes: 0

John Montgomery
John Montgomery

Reputation: 7106

You don't need to use filter for this. To remove an element at a specific index, just use array.splice(index, 1).

const words = ['One', 'Two', 'myWord', 'Three', 'myWord', 'Four']
words.splice(2, 1)
console.log(words)

const words2 = ['One', 'Two', 'myWord', 'Three', 'myWord', 'Four']
words2.splice(4, 1)
console.log(words2)

Upvotes: 1

wilbur
wilbur

Reputation: 395

Since the items in your array are identical, indexOf always returns 0 for each item filtered. 0 != 1 always evaluates to true. Since you always return true from filter, you effectively are doing words.filter(item => true) and filtering nothing.

May I ask what your intention is here? are you trying to uniqueify the array?

Upvotes: 0

Unmitigated
Unmitigated

Reputation: 89497

You can check if the index of an element is equal to the index of its first occurrence and keep only those elements.

words = ['myWord', 'myWord'];

words = words.filter((item,idx) => words.indexOf(item) === idx);

console.log(words);

You could also use a Set, which is a more efficient data structure that doesn't allow duplicates.

words = ['myWord', 'myWord'];

words = [...new Set(words)];

console.log(words);

Upvotes: 1

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