CODEWITHSUNDEEP
javascriptarrayssorting
Prosto Trader
Prosto Trader

Reputation: 3527

Does .sort function change original array?

I have that code:

arr = arr.sort(function (a, b) {
    return a.time>b.time
})

Do I need to redefine arr or it is possible just to call sort function? like this:

arr.sort(function (a, b) {
    return a.time>b.time
})

Will the sort and filter functions change the original array?

Upvotes: 56

Views: 50564

Answers (6)

Rohìt Jíndal
Rohìt Jíndal

Reputation: 27242

Will the sort and filter functions change the original array

For sort() method, Answer is Yes but for filter() method answer is No.

Let me explain with an example :

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

// Sorting array values and assigned in a variable.
const sortedArr = arr.sort((a, b) => a-b);

// Original array modified.
console.log(arr); // [1,2,3,4,5]

// New variable with sorted array.
console.log(sortedArr); // [1,2,3,4,5]

To prevent the original array to get modified, We can use to[Operation] that return a new collection with the operation applied (This is currently at stage 3, will be available soon).

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

const sortedArr = arr.toSort((a, b) => a-b);

console.log(arr); // [5, 4, 3, 2, 1]

console.log(sortedArr); // [1, 2, 3, 4, 5]

Upvotes: 1

Adrian Bartholomew
Adrian Bartholomew

Reputation: 2632

Or from ES6:

const a = [1, 2, 3];
const b = [...a].sort();

Upvotes: 2

SUSEENDHAR LAL
SUSEENDHAR LAL

Reputation: 141

Yes it modifies the original array.

const a = [1, 2, 3];
const b = a.sort();
const c = [...a].sort(); //es6 feauture similar to slice(0)
console.log(a === b); // true
console.log(a === c);//false

Upvotes: 5

Alexander Mills
Alexander Mills

Reputation: 100486

It's a decent question, and let's answer it properly:

const a = [1, 2, 3];
const b = a.sort();
console.log(a === b); // true

there is your answer. The === operator for objects will compare memory locations, so it's the same object in memory.

Which is a shame because it would be better if sort created a new array (immutability etc), but in many languages it does not return a new array, but the same array (reordered).

So if you want it to be immutable, you can do:

const a = [1, 2, 3];
const b = a.slice(0).sort();

Upvotes: 23

LexJacobs
LexJacobs

Reputation: 2533

Use slice() to sort a copy of the original array.

var arr =[{time:4},{time:3},{time:6}];

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

will mutate the original array and returns :

[ { time: 3 }, { time: 4 }, { time: 6 } ]

and console.log(arr) returns

[ { time: 3 }, { time: 4 }, { time: 6 } ]

but 

var arr =[{time:4},{time:3},{time:6}];
arr.slice().sort(function (a, b) {
  return a.time-b.time;
});

returns

[ { time: 3 }, { time: 4 }, { time: 6 } ]

but will not affect the original array.

console.log(arr) returns

[ { time: 4 }, { time: 3 }, { time: 6 } ]

Upvotes: 76

jfriend00
jfriend00

Reputation: 708156

It sorts the array in place (modifying the array). From MDN:

The sort() method sorts the elements of an array in place and returns the array. The sort is not necessarily stable. The default sort order is according to string Unicode code points.

Upvotes: 10

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