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How to insert an item into an array at a specific index?

tags2k
1#
tags2k Published in 2009-02-25 14:29:30Z

I am looking for a Javascript array insert method, in the style of:

arr.insert(index, item)

Preferably in jQuery, but any Javascript implementation will do at this point.

tvanfosson
2#
tvanfosson Reply to 2016-07-14 20:14:41Z

What you want is the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).

In this example we will create an array and add an element to it into index 2:

var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";

console.log(arr.join());
arr.splice(2, 0, "Lene");
console.log(arr.join());

The output of the code above will be:

Jani,Hege,Stale,Kai Jim,Borge
Jani,Hege,Lene,Stale,Kai Jim,Borge
Community
3#
Community Reply to 2017-05-23 12:10:47Z

If you want to insert multiple elements into an array at once check out this Stack Overflow answer: A better way to splice an array into an array in javascript

Also here are some functions to illustrate both examples:

function insertAt(array, index) {
    var arrayToInsert = Array.prototype.splice.apply(arguments, [2]);
    return insertArrayAt(array, index, arrayToInsert);
}

function insertArrayAt(array, index, arrayToInsert) {
    Array.prototype.splice.apply(array, [index, 0].concat(arrayToInsert));
    return array;
}

Finally here is a jsFiddle so you can see it for youself: http://jsfiddle.net/luisperezphd/Wc8aS/

And this is how you use the functions:

// if you want to insert specific values whether constants or variables:
insertAt(arr, 1, "x", "y", "z");

// OR if you have an array:
var arrToInsert = ["x", "y", "z"];
insertArrayAt(arr, 1, arrToInsert);
Sami
4#
Sami Reply to 2017-03-09 11:11:06Z

You can implement the Array.insert method by doing this:

Array.prototype.insert = function ( index, item ) {
    this.splice( index, 0, item );
};

Then you can use it like:

var arr = [ 'A', 'B', 'D', 'E' ];
arr.insert(2, 'C');

// => arr == [ 'A', 'B', 'C', 'D', 'E' ]
VisioN
5#
VisioN Reply to 2013-04-05 16:44:15Z

Custom array insert methods

1. With multiple arguments and chaining support

/* Syntax:
   array.insert(index, value1, value2, ..., valueN) */

Array.prototype.insert = function(index) {
    this.splice.apply(this, [index, 0].concat(
        Array.prototype.slice.call(arguments, 1)));
    return this;
};

It can insert multiple elements (as native splice does) and supports chaining:

["a", "b", "c", "d"].insert(2, "X", "Y", "Z").slice(1, 6);
// ["b", "X", "Y", "Z", "c"]

2. With array-type arguments merging and chaining support

/* Syntax:
   array.insert(index, value1, value2, ..., valueN) */

Array.prototype.insert = function(index) {
    index = Math.min(index, this.length);
    arguments.length > 1
        && this.splice.apply(this, [index, 0].concat([].pop.call(arguments)))
        && this.insert.apply(this, arguments);
    return this;
};

It can merge arrays from the arguments with the given array and also supports chaining:

["a", "b", "c", "d"].insert(2, "V", ["W", "X", "Y"], "Z").join("-");
// "a-b-V-W-X-Y-Z-c-d"

DEMO: http://jsfiddle.net/UPphH/

Ville
6#
Ville Reply to 2015-12-04 18:36:05Z

Even though this has been answered already, I'm adding this note for an alternative approach..

I wanted to place a known number of items into an array, into specific postitions, as they come off of an "associative array" (i.e. an object) which by definition is not guaranteed to be in a sorted order. I wanted the resulting array to be an array of objects, but the objects to be in a specific order in the array since an array guarantees their order. So I did this..

First the source object, a JSONB string retrieved from PostgreSQL. I wanted to have it sorted by the "order" property in each child object.

var jsonb_str = '{"one": {"abbr": "", "order": 3}, "two": {"abbr": "", "order": 4}, "three": {"abbr": "", "order": 5}, "initialize": {"abbr": "init", "order": 1}, "start": {"abbr": "", "order": 2}}';

var jsonb_obj = JSON.parse(jsonb_str);

Since the number of nodes in the object is known, I first create an array with the specified length:

var obj_length = Object.keys(jsonb_obj).length;
var sorted_array = new Array(obj_length);

And then iterate the object, placing the newly created temporary objects into the desired locations in the array without really any "sorting" taking place.

for (var key of Object.keys(jsonb_obj)) {
  var tobj = {};
  tobj[key] = jsonb_obj[key].abbr;

  var position = jsonb_obj[key].order - 1;
  sorted_array[position] = tobj;
}

console.dir(sorted_array);
Redu
7#
Redu Reply to 2016-05-22 21:43:29Z

For proper functional programming and chaining purposes an invention of Array.prototype.insert() is essential. Actually splice could have been perfect if it had returned the mutated array instead of a totally meaningless empty array. So here it goes

Array.prototype.insert = function(i,...rest){
  this.splice(i,0,...rest)
  return this
}

var a = [3,4,8,9];
document.write("<pre>" + JSON.stringify(a.insert(2,5,6,7)) + "</pre>");

Well ok the above with the Array.prototype.splice() one mutates the original array and some might complain like "you shouldn't modify what doesn't belong to you" and that might turn out to be right as well. So for the public welfare i would like to give another Array.prototype.insert() which doesn't mutate the original array. Here it goes;

Array.prototype.insert = function(i,...rest){
  return this.slice(0,i).concat(rest,this.slice(i));
}

var a = [3,4,8,9],
    b = a.insert(2,5,6,7);
console.log(JSON.stringify(a));
console.log(JSON.stringify(b));

Gaafar
8#
Gaafar Reply to 2016-07-04 09:18:02Z

Other than splice, you can use this approach which will not mutate the original array, but will create a new array with the added item. You should usually avoid mutation whenever possible. I'm using ES6 spread operator here.

const items = [1, 2, 3, 4, 5]

const insert = (arr, index, newItem) => [
  // part of the array before the specified index
  ...arr.slice(0, index),
  // inserted item
  newItem,
  // part of the array after the specified index
  ...arr.slice(index)
]

const result = insert(items, 1, 10)

console.log(result)
// [1, 10, 2, 3, 4, 5]

This can be used to add more than one item by tweaking the function a bit to use the rest operator for the new items, and spread that in the returned result as well

const items = [1, 2, 3, 4, 5]

const insert = (arr, index, ...newItems) => [
  // part of the array before the specified index
  ...arr.slice(0, index),
  // inserted items
  ...newItems,
  // part of the array after the specified index
  ...arr.slice(index)
]

const result = insert(items, 1, 10, 20)

console.log(result)
// [1, 10, 20, 2, 3, 4, 5]

hannad rehman
9#
hannad rehman Reply to 2017-05-18 07:05:26Z

This:

var arr= ["India","China","Japan","USA"];

arr.splice(index, 0, item);

Will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).

Pawan
10#
Pawan Reply to 2017-03-08 06:35:23Z

I tried this and it is working fine!!!!

var initialArr = ["India","China","Japan","USA"];
initialArr.splice(index, 0, item);

Index is the position where you want to insert or delete the element. 0 i.e the second parameters defines the number of element from the index to be removed item are the new entries which you want to make in array. It can be one or more than one.

initialArr.splice(2, 0, "Nigeria");
initialArr.splice(2, 0, "Australia","UK");
kind user
11#
kind user Reply to 2017-04-05 17:06:58Z

Another possible solution, with usage of Array#reduce.

var arr = ["apple", "orange", "raspberry"],
    arr2 = [1, 2, 4];

function insert(arr, item, index) {
    arr = arr.reduce(function(s, a, i) {
      i == index ? s.push(item, a) : s.push(a);
      return s;
    }, []);   
    console.log(arr);
}

insert(arr, "banana", 1);
insert(arr2, 3, 2);

Alireza
12#
Alireza Reply to 2017-12-27 19:41:30Z

I recommend using JavaScript in this case, also there is no insert method in JavaScript, but we have a method on built-in Array which does the job, it's called splice...

Let's see what's splice()...

The splice() method changes the contents of an array by removing existing elements and/or adding new elements.

OK, imagine we have this array below:

const arr = [1, 2, 3, 4, 5];

We can remove 3 like this:

arr.splice(arr.indexOf(3), 1);

It will return 3, but if we check the arr now, we have:

[1, 2, 4, 5]

So far, so good, but how we can add a new element to array using splice? Let's put back 3 in the arr...

arr.splice(2, 0, 3);

Let's see what we have done...

We use splice again, but this time for the second argument, we pass 0, means we want to delete no item, but at the same time, we add third argument which is 3 that will be added at second index...

You should be aware, that we can delete and add at the same time, for example now we can do:

 arr.splice(2, 2, 3);

Which will delete 2 items at index 2, then add 3 at index 2 and result will be:

[1, 2, 3, 5];

This is showing how each items in splice work:

array.splice(start, deleteCount, item1, item2, item3 ...)

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