Remove array elements by index

Question

I seem to be having a brain-freeze and am unable to remove JS array elements by index. Is there something fundamentally idiotic in the below?

var els;
[0, 1, 3]
0: 0
1: 1
2: 3


["Colour", "Font", "Icon", "Line 1"]
0: "Colour"
1: "Font"
2: "Icon"
3: "Text"

All I want to do is remove the elements from the array using index positions 0, 1 and 3 (in this example) - however, when I try this using splice, it messes up the indexes.

See:

els.each(function(key, val) {
            console.log(key);
            req-fields.splice(key,1);
        });

Richard Hamilton · Accepted Answer · 2015-12-03 21:44:24Z

3

Try something like this

function removeIndex(array, index) {
    delete array[index];
    array = array.filter(function(element) {
        return element != undefined
    });
    return array;
}

Example

removeIndex([1,4,7,13,41,16],3);
=> [1,4,7,41,16]

Explanation

To delete an element from an array, you use the delete keyword. This will make the value at that index undefined. You then need to filter the array, and remove undefined elements.

answered Dec 3, 2015 at 21:44

Richard Hamilton

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1 Comment

bsod99 Over a year ago

This is the one. Surprised to have to write a custom function for something like this, but there we go. Many thanks!

Katana314 · Accepted Answer · 2015-12-03 22:08:55Z

1

Variation on Richard Hamilton's. Note that both of ours will return a new array, not actually modify the original array object.

function removeIndexes(array, indexes) {
    return array.filter(function(element, i) {
        return indexes.indexOf(i) === -1;
    });
}

answered Dec 3, 2015 at 22:08

Katana314

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1 Comment

apollo Over a year ago

Richard Hamilton's modify the original: delete array[index] leaves a hole in the original array. var a = [0,1,2,3]; delete a[2]; a becomes [0,1, empty, 3]

Nina Scholz · Accepted Answer · 2015-12-04 07:03:41Z

1

You can adjust the index of the splice for every splicing action.

var fields = ["Colour", "Font", "Icon", "Line 1"],
    els = [0, 1, 3];

els.forEach(function (val, i) {
    fields.splice(val - i, 1);
});

document.write('<pre>' + JSON.stringify(fields, 0, 4) + '</pre>');

edited Dec 4, 2015 at 7:03

answered Dec 3, 2015 at 21:56

Nina Scholz

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Comments

Jeff · Accepted Answer · 2015-12-03 21:55:29Z

0

The issue is when you remove element 0, the array gets shifted down by 1 and your other elements are in the wrong positions. One way to solve this would be to sort your input els array in descending order so it will pop element 3, then 1, then 0.

els.sort(function(a, b){return b-a});

els.each(function(key, val) {
        console.log(key);
        req-fields.splice(key,1);
    });

answered Dec 3, 2015 at 21:55

Jeff

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