How to copy TypedArray into another TypedArray?

Question

C# has a high performance array copying function to copy arrays in place:

Array.Copy(source, destination, length)

It's faster than doing it manually ie.:

for (var i = 0; i < length; i++)
    destination[i] = source[i];

I am looking for an equivalent high performance copy function to copy arrays in place, for Int32Array and Float32Array in JavaScript and can find no such function:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

The closest is copyWithin which only does a copy internally within an array.

Is there a built in high performance copy function for TypedArrays in place?

Plan B, is there a built in high performance clone function instead? (EDIT: looks like slice() is the answer to that)

@علاء الدين, Array.join? that does not even return an array. — trincot
– trincot, Commented Feb 22, 2016 at 21:01
@MikeMcCaughan I disagree that this question is a duplicate. This question asks first and foremost how to copy values into an existing array, while that question asks how to create a new array. (This question tolerates the creation of a new array only as a last resort.) In this case, the answer appears to be .set; in that case the answer is .slice. Nevertheless, I think that other question is a helpful pointer. — apsillers
– apsillers, Commented Feb 22, 2016 at 21:14
Can we get a sample data set to compare the answers in a performance test? — Vinny M
– Vinny M, Commented Feb 22, 2016 at 21:25

apsillers · Accepted Answer · 2016-02-22 21:16:24Z

50

You're looking for .set which allows you to set the values of an array using an input array (or TypedArray), optionally starting at some offset on the destination array:

destination.set(source);
destination.set(source, offset);

Or, to set a limited amount of the input array:

destination.set(source.slice(limit), offset);

If you instead want to create a new TypedArray, you can simply use .slice:

source.slice();

edited Feb 22, 2016 at 21:16

answered Feb 22, 2016 at 21:08

apsillers

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2 Comments

James Wilkins Over a year ago

BTW If you're looking for efficiency you might use source.subarray(limit) instead of slice so only a new view is created and the same underlying data store is used (no intermediate data copy required).

Waruyama Over a year ago

It is really unfortunate that TypesArray.set() does not accept an optional third parameter to limit the number of entries to be copied. So currently creating an intermediate view using source.subarray(limit) seems to be the way to go.

Vinny M · Accepted Answer · 2016-02-22 22:13:14Z

8

You can clone an array using slice(0);.

var clone = myArray.slice(0);

And you can make it a native method:

Array.prototype.clone = function() {
    return this.slice(0);
};

Performance link comparing to loop

edited Feb 22, 2016 at 22:13

answered Feb 22, 2016 at 20:52

Vinny M

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6 Comments

trincot Over a year ago

slice is the way to go. If that ain't high performance enough, then the downvoter should downvote JavaScript, not the messenger.

Heretic Monkey Over a year ago

You don't need to 0. See the duplicate: stackoverflow.com/q/7486085/215552

Vinny M Over a year ago

@MikeMcCaughan, actually the 0 runs faster, and this was a performance question.

Brendan Hill Over a year ago

Thanks, actually for good reasons my preference is to copy into an existing array "in place" to minimize memory volatility and having to update references. Hence slice() is undesirable. The performance link seems to be for JS arrays, not TypedArrays.

Jack G Over a year ago

Please do not extend the native array. It is much much slower than just doing .slice(0).

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cuixiping · Accepted Answer · 2016-03-25 15:23:44Z

6

clone to an exist typedarray:

destination.set(source);
destination.set(source, offset);

clone to a new typedarray example: (It's fastest!)

var source = new Uint8Array([1,2,3]);
var cloned = new Uint8Array(source);

answered Mar 25, 2016 at 15:23

cuixiping

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1 Comment

Lazerbeak12345 Over a year ago

About using the constructor, good tip. Though I'd like to point out that if the cloned array already exists (ex you are using a double-buffer setup) then .set is (by my measurement) 20 times faster (1.5 ms self time vs 29.8 ms self time), as it does not need to allocate memory. (My test involved a pair of Uint32Arrays each with 10,000 items, containing semi-random data in a real-world use-case)

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