Chunking an Array in JavaScript: Four Ways Compared

Chunking an array means splitting it into smaller arrays of a specified size. This is useful for data processing, pagination, and more. We’ll explore four methods to chunk an array and compare their performance.

First, let’s create an array of numbers from 1 to 10:

const arr = Array.from({ length: 10 }, (_, i) => i + 1);

Array.from() is used to generate an array with elements from 1 to 10.
Now, we’ll look at four ways to chunk this array.

Method 1: Using a For Loop

function chunkArr(arr, size) {
 let res = [];
 for (let i = 0; i < arr.length; i += size) {
 res.push(arr.slice(i, size + i));
 }
 return res;
}

console.time("for");
console.log(chunkArr(arr, 2));
console.timeEnd("for");

Output:

[ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ], [ 9, 10 ] ]
for: 4.363ms

Explanation: This function iterates through the array in steps of the specified chunk size. It slices the array at each step and adds the resulting sub-array to the result array (res). The performance measurement shows it took about 4.363 milliseconds.

Method 2: Using Array.reduce()

function chunkArr2(arr, size) {
 if (size <= 0) throw new Error('Chunk size must be a positive integer');
 return arr.reduce((acc, _, i) => {
 if (i % size === 0) acc.push(arr.slice(i, i + size));
 return acc;
 }, []);
}
console.time("reduce");
console.log(chunkArr2(arr, 2));
console.timeEnd("reduce");

Output:

[ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ], [ 9, 10 ] ]
reduce: 0.069ms

Explanation: Here Array.reduce() is used to build the chunked array. It checks if the current index is a multiple of the chunk size and slices the array accordingly. This method is significantly faster, taking only about 0.069 milliseconds.

Method 3: Using Array.splice()

let [list, chunkSize] = [arr, 2];
console.time('splice');
list = […Array(Math.ceil(list.length / chunkSize))].map(_ => list.splice(0, chunkSize));
console.timeEnd('splice');
console.log(list);

Output:

[ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ], [ 9, 10 ] ]
splice: 0.048ms

Explanation: This approach uses Array.splice() in combination with Array.map() to chunk the array. It creates a new array with the required number of chunks and uses splice() to remove and collect chunks from the original array. This method is also very fast, taking about 0.048 milliseconds.

Method 4: Recursive Approach

const chunk = function(array, size) {
 if (!array.length) {
 return [];
 }
 const head = array.slice(0, size);
 const tail = array.slice(size);
return [head, …chunk(tail, size)];
};

console.time(‘recursive’);
console.log(chunk(arr, 2));
console.timeEnd(‘recursive’);

Output:

[ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ], [ 9, 10 ] ]
recursive: 4.372ms

Explanation: This recursive method splits the array into the first chunk (head) and the remaining elements (tail). It then recursively processes the tail, concatenating the results. While more elegant, this method is slower than the reduce and splice methods, taking about 4.372 milliseconds.

Conclusion
All four methods successfully chunk the array into sub-arrays of the specified size. However, their performance varies significantly:

1. For Loop: 4.363ms
2. Reduce: 0.069ms
3. Splice: 0.048ms
4. Recursive: 4.372ms

The splice and reduce methods are the fastest, making them preferable for performance-critical applications. While functional, the for loop and recursive methods are slower and might be less suitable for large datasets.

Depending on your needs and readability preferences, you can choose a suitable method for chunking arrays in your JavaScript projects.

You can find more approach here

And Finally,
Please don’t hesitate to point out any mistakes in my writing and any errors in my logic.

I’m appreciative that you read my piece.