Benchmark: Mutate array vs memory efficient map

Mutate array vs memory efficient map (version: 1)

In memory constrained devices the use of .map() is not always possible. In such places, this should determine whether a mutation is better than creating a new array from scratch while emptying the original array, thus, keeping somewhat the same memory usage.

Comparing performance of: Mutate array vs Memory efficient map

Created: one month ago by: Guest

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Script Preparation code:

var test = [];

for (let i = 0; i < 100000; i++) {
  test.push(i);
}

Tests:

Mutate array
for (let i = 0; i < test.length; i++) { test[i] = i * 2; }
Memory efficient map
const copyTest = test.map((item) => item * 2);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Mutate array
Memory efficient map

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one month ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36

Browser/OS: Chrome 130 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Mutate array	115.7 Ops/sec
Memory efficient map	3634.8 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):

LLMs can make mistakes. Check important info.

### Benchmark Overview

The provided benchmark compares two different approaches for transforming an array of integers: **mutating the original array** and using **the `map` method** to create a new array with the transformed values. This comparison is particularly relevant in environments with **memory constraints**, where memory usage efficiency can be a critical factor.

#### Options Compared

1. **Mutate Array**
   - **Code Snippet**: 
     ```javascript
     for (let i = 0; i < test.length; i++) {
       test[i] = i * 2;
     }
     ```
   - **Description**: This approach involves iterating over the original `test` array and directly modifying its elements. Each element is replaced with the result of the expression `i * 2`.

2. **Memory Efficient Map**
   - **Code Snippet**: 
     ```javascript
     const copyTest = test.map((item) => item * 2);
     ```
   - **Description**: Here, the `map` method is utilized to create a new array called `copyTest`, where each element is the result of the transformation applied to the original `test` array. This may result in higher memory usage due to the creation of a new array, depending on the size of the original array.

### Pros and Cons

#### Mutate Array
- **Pros**:
  - **Memory Efficiency**: Since it modifies the existing array in place, it avoids the creation of a new array, leading to lower memory usage.
  - **Simplicity**: The code is straightforward and easy to understand, especially in scenarios where array length is fixed.
  
- **Cons**:
  - **Loss of Original Data**: The original data in the array is lost after mutation, which may not be acceptable in many situations where immutability is desired.
  - **Potential Side Effects**: If other parts of the code rely on the original array data, this mutation could lead to unintended consequences.

#### Memory Efficient Map
- **Pros**:
  - **Immutability**: It preserves the original array, allowing developers to maintain the initial state, which is beneficial in many contexts, especially in functional programming paradigms.
  - **Readability**: The intention to transform data is very clear, as `map` is a descriptive and commonly used method in JavaScript.

- **Cons**:
  - **Higher Memory Usage**: Depending on the size of the original array, this approach may create significant additional memory overhead for the new array.
  - **Performance Overhead**: In memory-constrained environments, the overhead of creating a new array can hamper performance and speed, as indicated by the benchmark results.

### Benchmark Results Summary
From the benchmark results, we see that the **Memory efficient map** approach executed at approximately **3635 executions per second**, while the **Mutate array** strategy achieved only about **116 executions per second**. This stark contrast shows that while mutation can be more memory efficient, it suffers significantly in terms of execution speed compared to the more modern `map` method, even though it is typically faster for sheer number of operations in typical environments.

### Other Considerations
When deciding on which method to use, software engineers should consider the specific requirements of their application:
- **Memory Constraints**: If the application needs to run on devices with limited memory (like mobile devices), the mutate approach may be preferable.
- **Data Integrity**: If preserving the original dataset is crucial, the map approach should be preferred irrespective of performance costs.

### Alternatives
Other alternatives for array transformations include:
- **`forEach` method**: Similar to `map`, but does not return a new array. It can be used for applying a function to each element while allowing for mutation.
- **`reduce` method**: Transform the array into a single value, which can also help to build new arrays or objects while maintaining control over memory usage.
- **Spread Operator**: While not a direct replacement for `map`, spread (`...`) can be used in conjunction with other methods to create new arrays in a concise manner.

In conclusion, the decision between mutating an array or using the `map` method depends on the specific context, ensuring a careful balance between performance and data management principles.

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