Benchmark: flatMap vs reduce using push spread

Script Preparation code:

var arr = Array(10_000).fill({arr: [0,1]})

Tests:

reduce with concat
arr.reduce((acc, x) => {acc.push(...x.arr); return acc}, [])
flatMap
arr.flatMap(x => x.arr)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
reduce with concat
flatMap

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's break down the provided benchmark and explain what's being tested.

**Benchmark Overview**

The test compares two approaches: using `reduce()` with `concat` (or equivalently, `.push()`) versus using `flatMap()` on an array of arrays.

**Script Preparation Code**
```javascript
var arr = Array(10_000).fill({arr: [0,1]});
```
This code creates a large array (`arr`) containing 10,000 objects, each with an `arr` property that contains two elements: `[0, 1]`.

**Benchmark Definitions**

There are two benchmark definitions:

1. **"reduce with concat"**
```javascript
arr.reduce((acc, x) => { acc.push(...x.arr); return acc }, []);
```
This code uses the `reduce()` method to iterate over the array and push each element of the nested arrays into a new array (`acc`). The resulting array is then returned.

2. **"flatMap"**
```javascript
arr.flatMap(x => x.arr);
```
This code uses the `flatMap()` method, which is a more modern replacement for `.concat()` with `.map()`. It returns a new array with the elements of each nested array, without creating intermediate arrays.

**Library and Special Features**

In this benchmark, we're using JavaScript's built-in Array methods:

* `.reduce()`
* `.flatMap()`
* `.push()`

No external libraries are used in this test.

**Approach Comparison**

The two approaches have different performance characteristics:

1. **"reduce with concat"**: This approach uses a simple iterative method to build the result array, which can be slower due to the overhead of function calls and array concatenation.
2. **"flatMap"**: This approach is generally faster because it avoids the need for explicit iteration and array concatenation. However, modern browsers have optimized `flatMap()` to perform similarly to `.concat()`, so the performance difference may be smaller than expected.

**Pros and Cons**

* **"reduce with concat"**:
	+ Pros: straightforward implementation, easy to understand.
	+ Cons: slower due to array concatenation.
* **"flatMap"**:
	+ Pros: faster, more modern method, less prone to errors.
	+ Cons: may require more time to understand, depends on browser optimizations.

**Other Considerations**

When choosing between these approaches, consider the following:

* If you need to process a large array with nested elements and don't care about performance, `reduce()` might be a better choice due to its simplicity.
* If performance is critical and you're using modern browsers that support `flatMap()`, this method may be a better option.

**Alternatives**

Other methods for flattening arrays include:

1. **`.map()`: arr.map(x => x.arr).flat()**
2. **`.forEach()`**: arr.forEach(x => { const result = [...x.arr]; // do something with result });
3. **Looping manually using `for` and array indexing**

Related benchmarks:

flatMap vs reduce using push spread (version: 0)

Comparing performance of: reduce with concat vs flatMap

Created: 4 years ago by: Guest

Jump to the latest result

reduce with concat

flatMap

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):