NOTES.md

Explanation: 2635. Apply Transform Over Each Element In Array

Key Topics

Arrays, Higher-Order Functions

Problem In My Own Words

Create a function that takes an array and a function where the function would be applied to every single element of the array and a new array would be returned with the new values. It should be solved without the Array.map method and should pass the current element's value arr[i] and index number i to the transformation function (returnedArray[i] = fn(arr[i], i)).

Final Solution

• Time Complexity: O(n) where n is the length of the array that is passed. Because each element in the array will be iterated through, the time complexity is dependent on the number of items.

const map = function (arr, fn) {
	const newArray = [];

	for (let i = 0; i < arr.length; i++) {
		const newValue = fn(arr[i], i);
		newArray.push(newValue);
	}

	return newArray;
};

Process

The map function transforms an array by:

1. Creating an empty array to store the new values.
2. Iterating through each element of the original array.
3. Applying a function to each element.
4. Storing the transformed values in the new array.

For example, if we start with the array [1, 2, 3, 4, 5] and pass the function fn = (x) => x + 2, the map function will:

• Loop through each element
• Apply the function to transform each value
• Store each new value in a new array

The original array remains untouched, and we receive a new array [3, 4, 5, 6, 7].

Test Cases

// Basic transformation
map([1, 2, 3, 4, 5], x => x + 2); // [3, 4, 5, 6, 7]

// Transformation using the index number
map([10, 20, 30], (x, i) => x + i); // [10, 21, 32]

Resources

• MDN Web Documentation: Array.prototype.map()