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Loop to remove an element in array with multiple occurrences

scottt
Eduen Sarceno

I want to remove an element in an array with multiple occurrences with a function.

var array=["hello","hello","world",1,"world"];

function removeItem(item){
    for(i in array){
        if(array[i]==item) array.splice(i,1);
    }
}

removeItem("world");
//Return hello,hello,1

removeItem("hello");
//Return hello,world,1,world

This loop doesn’t remove the element when it repeats twice in sequence, only removes one of them.

Why?

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Answer

You have a built in function called filter that filters an array based on a predicate (a condition).

It doesn’t alter the original array but returns a new filtered one.

var array=["hello","hello","world",1,"world"];
var filtered = array.filter(function(element) {
    return element !== "hello";
}); // filtered contains no occurrences of hello

You can extract it to a function:

function without(array, what){
    return array.filter(function(element){ 
        return element !== what;
    });
}

However, the original filter seems expressive enough.

Here is a link to its documentation

Your original function has a few issues:

  • It iterates the array using a for... in loop which has no guarantee on the iteration order. Also, don’t use it to iterate through arrays – prefer a normal for... loop or a .forEach
  • You’re iterating an array with an off-by-one error so you’re skipping on the next item since you’re both removing the element and progressing the array.