I have var ar = [1, 2, 3, 4, 5] and want some function getSubarray(array, fromIndex, toIndex), that result of call getSubarray(ar, 1, 3) is new array [2, 3, 4].
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11Have you tried slice?Tom Knapen– Tom Knapen2011-09-24 10:48:40 +00:00Commented Sep 24, 2011 at 10:48
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5 Answers
Take a look at Array.slice(begin, end)
const ar = [1, 2, 3, 4, 5];
// slice from 1..3 - add 1 as the end index is not included
const ar2 = ar.slice(1, 3 + 1);
console.log(ar2); // -> [2, 3, 4]
// the original ar is unmodified.
console.log(ar); // -> [1, 2, 3, 4, 5]
5 Comments
daemone
It's probably worth explicitly mentioning here that the original
ar is unmodified. console.log(ar); // -> [1, 2, 3, 4, 5]
Vladimir Fokow
Also, don't make the mistake of confusing the
slice() method with splice(): splice() changes the original array while slice() doesn't.
Igor
I'm sorry, but what if I try to slice using parameters, that'd raise some sort of "index out of bounds" error? In the example imagine I'd go with
ar.slice(4, 4);? I guess I should try out :x..
JM217
@Igor No, slice does not raise an exception. If the
end is greater than the length of the sequence, slice extracts through to the end of the sequence (arr.length). developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…JM217
I want to add another note that
slice does not raise exceptions for any type of input (string, undefined, object whatever). If start is out of range (negative or greater than the length), it just returns an empty array.For a simple use of slice, use my extension to Array Class:
Array.prototype.subarray = function(start, end) {
if (!end) { end = -1; }
return this.slice(start, this.length + 1 - (end * -1));
};
Then:
var bigArr = ["a", "b", "c", "fd", "ze"];
Test1:
bigArr.subarray(1, -1);
< ["b", "c", "fd", "ze"]
Test2:
bigArr.subarray(2, -2);
< ["c", "fd"]
Test3:
bigArr.subarray(2);
< ["c", "fd","ze"]
Might be easier for developers coming from another language (i.e. Groovy).
answered Aug 21, 2013 at 13:50
Abdennour TOUMI
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3 Comments
Kartik Chugh
daemone
What K_7 said; most especially, monkey-patching the Builtins (Object, Array, Promise, etc) is very naughty. See the famous example of MooTools forcing a rename of the proposed native
Array.prototype.contains to Array.prototype.includes.daemone
Not to mention, your
subarray method delivers unexpected results. bigArr.slice(1,-1) returns ['b','c','fd'], which you would expect (the -1 knocks one element off the end of the new array). But bigArr.subarray(1,-1) returns the same as bigArr.subarray(1), which is to say everything from position 1 to the end of bigArr. You're also forcing users to always give negative numbers as the end parameter. Any end >= -1 gives the same result as when end === undefined. On the other hand, bigArr.slice(1,3) returns ['b','c'], which again is expected.I have var ar = [1, 2, 3, 4, 5] and want some function getSubarray(array, fromIndex, toIndex), that result of call getSubarray(ar, 1, 3) is new array [2, 3, 4].
Exact Solution
function getSubarray(array, fromIndex, toIndex) {
return array.slice(fromIndex, toIndex+1);
}
Let's Test the Solution
let ar = [1, 2, 3, 4, 5]
getSubarray(ar, 1, 3)
// result: [2,3,4]
Array.prototype.slice()
The slice() method returns a shallow copy of a portion of an array into a new array object selected from start to end (end not included) where start and end represent the index of items in that array. The original array will not be modified.
Basically, slice lets you select a subarray from an array.
For example, let's take this array:
const animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];
Doing this:
console.log(animals.slice(2, 4));
Will give us this output:
// result: ["camel", "duck"]
Syntax:
slice() // creates a shallow copy of the array
slice(start) // shows only starting point and returns all values after start index
slice(start, end) // slices from start index to end index
Comments
const array_one = [11, 22, 33, 44, 55];
const start = 1;
const end = array_one.length - 1;
const array_2 = array_one.slice(start, end);
console.log(array_2);
1 Comment
bormat
it does not compile here the correction : var array_one = [11, 22, 33, 44,55]; var ar2 = array_one.slice(0, array_one.length-1); console.log(ar2)
The question is actually asking for a New array, so I believe a better solution would be to combine Abdennour TOUMI's answer with a clone function:
function clone(obj) {
if (null == obj || "object" != typeof obj) return obj;
const copy = obj.constructor();
for (const attr in obj) {
if (obj.hasOwnProperty(attr)) copy[attr] = obj[attr];
}
return copy;
}
// With the `clone()` function, you can now do the following:
Array.prototype.subarray = function(start, end) {
if (!end) {
end = this.length;
}
const newArray = clone(this);
return newArray.slice(start, end);
};
// Without a copy you will lose your original array.
// **Example:**
const array = [1, 2, 3, 4, 5];
console.log(array.subarray(2)); // print the subarray [3, 4, 5, subarray: function]
console.log(array); // print the original array [1, 2, 3, 4, 5, subarray: function][http://stackoverflow.com/questions/728360/most-elegant-way-to-clone-a-javascript-object]
4 Comments
Mani
I dont think that slice will change the original array.
Guido Bouman
Array.prototype.slice returns a copy already. Array.prototype.splice modifies the original array.
TheCrazyProgrammer
The slice() method returns a shallow copy of a portion of an array into a new array object. See Mozilla Developer Network. Downvoted.
daemone
As others have said,
slice already returns a shallow copy, making this subarray implementation unnecessary. But it's also worth mentioning you've monkey-patched a builtin object, which is a big no-no. See the comments on Abdennour TOUMI's answer.