Benchmark: slice vs new allocation

Script Preparation code:

var arr = [];
for (let i = 0; i < 1000000; i++) {
  arr.push(i);
}

Tests:

Slice
let a = []; for (let i = 0; i < 1000; i++) { a.push(arr.slice(i * 10, 1000)); }
Length - 1
let a = []; for (let i = 0; i < 1000; i++) { a.push(Array.from(arr.slice(i * 10, 1000))); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Slice
Length - 1

Fastest: N/A

Slowest: N/A

Latest run results:

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Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

Let's break down the benchmark and its test cases.

**Benchmark Definition**

The benchmark definition is a JSON object that describes the test case. In this case, it defines two test cases: "Slice" and "Length - 1". The script preparation code is provided to create an array `arr` with 1 million elements, and then populate it with values from 0 to 999999.

**Test Cases**

There are two test cases:

### Test Case 1: Slice

The benchmark definition for this test case is:
```javascript
let a = [];
for (let i = 0; i < 1000; i++) {
  a.push(arr.slice(i * 10, 1000));
}
```
This code creates an array `a` and then pushes to it 1000 slices of the original array `arr`, starting from index 10 to 9999. The `slice()` method is used to extract a subset of elements from `arr`.

### Test Case 2: Length - 1

The benchmark definition for this test case is:
```javascript
let a = [];
for (let i = 0; i < 1000; i++) {
  a.push(Array.from(arr.slice(i * 10, 1000)));
}
```
This code creates an array `a` and then pushes to it 1000 elements converted from the slices of `arr`, using the `Array.from()` method. The `slice()` method is still used to extract subsets of elements from `arr`.

**Comparison**

In both test cases, the goal is to measure the performance difference between slicing an array and using a different approach to create a new array.

**Options Compared**

The options compared are:

1. Slicing an array using `slice()`
2. Using `Array.from()` to convert slices of an array into a new array

**Pros and Cons**

* **Slicing an Array (Method 1)**:
	+ Pros: Efficient for large arrays, as it only copies the necessary elements.
	+ Cons: May be slower for small arrays due to the overhead of creating a slice object.
* **Using `Array.from()` (Method 2)**:
	+ Pros: Faster for small arrays due to the use of optimized array creation algorithms.
	+ Cons: May be slower for large arrays due to the need to create multiple intermediate arrays.

**Library and Special JS Feature**

Neither of these options relies on a specific JavaScript library or special feature. The `Array.from()` method is a standard method in modern JavaScript, introduced in ECMAScript 2015 (ES6).

**Considerations**

When choosing between slicing an array and using `Array.from()`, consider the size of the array and the performance requirements of your application.

* For large arrays, slicing may be more efficient due to the reduced overhead.
* For small arrays, using `Array.from()` may provide faster execution times.

**Other Alternatives**

There are other ways to create a new array from a slice or an original array:

1. Using `map()`: `arr.slice(i * 10, 1000).map(x => x)`
2. Using a `for...of` loop: `for (let i of arr.slice(i * 10, 1000)) { ... }`
3. Using `reduce()`: `arr.slice(i * 10, 1000).reduce((acc, curr) => acc.concat(curr), [])`

However, these alternatives may not be as efficient or expressive as slicing and using `Array.from()`.

I hope this explanation helps!

Related benchmarks:

slice vs new allocation (version: 0)

Comparing performance of: Slice vs Length - 1

Created: 3 years ago by: Guest

Jump to the latest result

Slice

Length - 1

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):