Benchmark: Map vs For Loop - MeasureThat.net

Script Preparation code:

var a = [];
for (var i = 0; i < 1e6; i++) {
  a[i] = Math.random();
}

Tests:

Map
var b = a.map(n => n * 2);
For Loop
var b = []; for (var i = 0; i < a.length; i++) { b[i] = a[i] * 2; }
foreach
var b = a.forEach(n => n * 2);
pre-allocated for loop
var b = new Array(a.length); for (var i = 0; i < a.length; i++) { b[i] = a[i] * 2; }
pre-allocated unrolled for loop
var b = new Array(a.length); for (var i = 0; i < a.length/4; i++) { b[i*4] = a[i*4] * 2; b[i*4+1] = a[i*4+1] * 2; b[i*4+2] = a[i*4+2] * 2; b[i*4+3] = a[i*4+3] * 2; }
++for loop
var b = new Array(a.length); for (var i = 0; i < a.length; ++i) { b[i] = a[i] * 2; }
--for loop
var b = new Array(a.length); for (var i = a.length; i >= 0; --i) { b[i] = a[i] * 2; }
for loop let
var b = []; for (let i = 0; i < a.length; i++) { b[i] = a[i] * 2; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Map
For Loop
foreach
pre-allocated for loop
pre-allocated unrolled for loop
++for loop
--for loop
for loop let

Fastest: N/A

Slowest: N/A

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

LLMs can make mistakes. Check important info.

Let's dive into the Benchmark Definition JSON and explain what is tested, compare options, pros and cons of each approach, and other considerations.

**Benchmark Definition**

The benchmark defines four test cases that aim to measure the performance difference between different ways of iterating over an array:

1. `Map`
2. `For Loop` (with traditional syntax)
3. `foreach`
4. `pre-allocated for loop`
5. `pre-allocated unrolled for loop`
6. `++for loop`
7. `--for loop`
8. `for loop let`

**Test Case Options**

Here's a brief description of each test case:

1. **Map**: Creates a new array using the `map()` method, where each element is multiplied by 2.
2. **For Loop (traditional)**: Iterates over the original array using a traditional `for` loop, multiplying each element by 2.
3. **foreach**: Uses the `forEach()` method to iterate over the original array, multiplying each element by 2. Note that `forEach()` does not return a new array, it modifies the original array.
4. **pre-allocated for loop**: Creates a new array with the same length as the original array and then iterates over it using a traditional `for` loop, multiplying each element by 2.
5. **pre-allocated unrolled for loop**: Similar to the previous option, but the loop iterates over every four elements at a time (e.g., `i*4`, `i*4+1`, etc.), multiplying corresponding elements by 2.
6. **++for loop**: Similar to the traditional `for` loop, but uses increment/decrement operators (`++`) to iterate.
7. **--for loop**: Similar to the previous option, but uses decrement operators (`--`) to iterate.
8. **for loop let**: Uses the `let` keyword with a traditional `for` loop to iterate over the original array, multiplying each element by 2.

**Performance Considerations**

The performance difference between these methods can be significant due to the following factors:

* Overhead of function calls (e.g., `map()`, `forEach()`): These methods have additional overhead compared to traditional loops.
* Array creation and modification: Creating a new array using `map()` or `forEach()` can be slower than iterating over an existing array with a traditional loop.
* Loop control: Traditional loops allow for more control over the iteration process, which can lead to better performance in certain scenarios.

**Pros and Cons of Each Approach**

Here's a brief summary of the pros and cons of each approach:

1. **Map**: Pros - concise code, easy to read; Cons - additional overhead due to function call.
2. **For Loop (traditional)**: Pros - control over iteration, no additional overhead; Cons - less readable than other options.
3. **foreach**: Pros - concise code, easy to read; Cons - modifies original array, may not be suitable for all use cases.
4. **pre-allocated for loop**: Pros - predictable performance, easy to optimize; Cons - requires extra memory allocation.
5. **pre-allocated unrolled for loop**: Pros - optimized performance, reduced overhead; Cons - more complex code.
6. **++for loop**: Pros - concise code, easy to read; Cons - less predictable than traditional loops.
7. **--for loop**: Pros - similar to traditional loop, but with decrement operators; Cons - less readable than traditional loop.
8. **for loop let**: Pros - concise code, easy to read; Cons - may not be suitable for all use cases due to variable scoping.

**Additional Observations**

* The `map()` and `forEach()` methods can be useful when you need to perform a transformation or side effect on each element of an array.
* Traditional loops (e.g., `for` loop) are generally more predictable and easier to optimize than other options.
* The use of `let` keywords with traditional loops can improve code readability and maintainability.

Overall, the choice of iteration method depends on the specific requirements and constraints of your use case.

Latest run results:

Run details: (Test run date: 7 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

Browser/OS: Chrome 55 on Windows

View result in a separate tab

Test name	Executions per second
Map	1.9 Ops/sec
For Loop	1.6 Ops/sec
foreach	18.0 Ops/sec
pre-allocated for loop	1.7 Ops/sec
pre-allocated unrolled for loop	2.7 Ops/sec
++for loop	1.7 Ops/sec
--for loop	1.6 Ops/sec
for loop let	1.6 Ops/sec

Related benchmarks:

Map vs For Loop (version: 0)

Comparing performance of: Map vs For Loop vs foreach vs pre-allocated for loop vs pre-allocated unrolled for loop vs ++for loop vs --for loop vs for loop let

Created: 7 years ago by: Guest

Jump to the latest result

Map

For Loop

foreach

pre-allocated for loop

pre-allocated unrolled for loop

++for loop

--for loop

for loop let

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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