Map, Filter and Reduce

Map

• Transforms Elements: The map function transforms each element of an array using a provided callback function.
• New Array Creation: It creates a new array with the transformed values.
• One-to-One Relationship: Maintains a one-to-one relationship between the original and transformed elements.

Syntax:

const newArray = array.map((element) => transformedElement);

Examples:

Doubling Numbers:

const numbers = [1, 2, 3, 4, 5];
const doubledNumbers = numbers.map((num) => num * 2);
console.log(doubledNumbers); // [2, 4, 6, 8, 10]

Capitalizing Strings:

const words = ['apple', 'banana', 'cherry'];
const capitalizedWords = words.map((word) => word.charAt(0).toUpperCase() + word.slice(1));
console.log(capitalizedWords); // ['Apple', 'Banana', 'Cherry']

 

Filter

• Creates New Array: The filter function creates a new array containing elements that satisfy a provided condition.
• Selective Inclusion: Acts as a selective mechanism, allowing only elements that meet the given criteria to be included in the new array.

Syntax:

const newArray = array.filter((element) => conditionIsTrue);

Examples:

Filtering Even Numbers:

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const evenNumbers = numbers.filter((num) => num % 2 === 0);
console.log(evenNumbers); // [2, 4, 6, 8, 10]

Filtering Words with Length > 5:

const words = ['apple', 'banana', 'cherry', 'date', 'elderberry'];
const longWords = words.filter((word) => word.length > 5);
console.log(longWords); // ['banana', 'cherry', 'elderberry']

 

Reduce

• Aggregates Elements: The reduce function aggregates the elements of an array into a single value based on a provided callback function.
• Iterative Accumulation: Iterates through the array, accumulating a result.
• Useful for Summary: Particularly useful for deriving a summary or a single value from an array.

Syntax:

const result = array.reduce((accumulator, current) => newAccumulatorValue, initialValue);

Examples:

Summing Numbers:

const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((accumulator, current) => accumulator + current, 0);
console.log(sum); // 15

Concatenating Strings:

const words = ['Hello', ' ', 'world', '!'];
const sentence = words.reduce((accumulator, current) => accumulator + current, '');
console.log(sentence); // ‘Hello world!’