Benchmark: Group by - reassign vs immutable

Script Preparation code:

var arr = [{
    id: "1",
    type: "a"
}, {
    id: "2",
    type: "a"
}, {
    id: "3",
    type: "b"
}, {
    id: "4",
    type: "b"
}, {
    id: "5",
    type: "a"
}]

Tests:

reassign
function groupBy( arr, key ) { return arr.reduce( (acc, cur) => ({ ...acc, [String(acc[key(cur)])]: [...(acc[key(cur)] || []), cur], }), {}, ); } groupBy(arr, (item) => item.type);
immutable
function groupBy( arr, key ) { return arr.reduce((groups, item) => { (groups[key(item)] ||= []).push(item); return groups; }, {}); } groupBy(arr, (item) => item.type);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
reassign
immutable

Fastest: N/A

Slowest: N/A

Latest run results:

No previous 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 provided benchmark and explain what's being tested, compared, and what pros and cons of each approach are.

**Benchmark Definition**

The benchmark is comparing two approaches to grouping an array by a specific key:

1. `reassign`: This approach modifies the original array in place, creating new arrays for each group.
2. `immutable`: This approach creates a new object to store the grouped data, without modifying the original array.

**Script Preparation Code**

The script preparation code defines an array of objects:
```javascript
var arr = [
  { id: "1", type: "a" },
  { id: "2", type: "a" },
  { id: "3", type: "b" },
  { id: "4", type: "b" },
  { id: "5", type: "a" }
];
```
This array is used to test both grouping approaches.

**Html Preparation Code**

There is no HTML preparation code provided, so we can assume that the benchmark only runs on the JavaScript side.

**Individual Test Cases**

The two individual test cases are:

1. `reassign`: This test case uses the `reassign` approach to group the array by the `type` key.
2. `immutable`: This test case uses the `immutable` approach to group the array by the `type` key.

**Library and Purpose**

There is no library explicitly mentioned in the benchmark definition. However, it appears that the `reduce()` method is being used to implement both grouping approaches.

**Special JS Feature or Syntax**

Neither of the test cases uses any special JavaScript features or syntax beyond the standard `reduce()` method.

**Pros and Cons of Each Approach**

Here's a brief summary:

1. `reassign`:
	* Pros: May be faster since it doesn't create new arrays, only modifies the original array.
	* Cons: Modifies the original array, which may not be desirable in some cases (e.g., when working with external data).
2. `immutable`:
	* Pros: Does not modify the original array, preserving its integrity.
	* Cons: May be slower since it creates new arrays for each group.

**Other Alternatives**

Other approaches to grouping an array by a specific key might include:

1. Using the `Array.prototype.forEach()` method and creating a new object to store the grouped data.
2. Using a library like Lodash's `groupBy()` function, which implements both `reassign` and `immutable` approaches internally.

Overall, this benchmark is designed to compare two common approaches to grouping an array by a specific key in JavaScript. The results can help developers understand the performance implications of each approach and choose the one that best fits their use case.

Related benchmarks:

Group by - reassign vs immutable (version: 0)

Comparing performance of: reassign vs immutable

Created: 3 years ago by: Guest

Jump to the latest result

reassign

immutable

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):