Cómo manipular matrices en JavaScript

Programación

Una parte importante de cualquier lenguaje de programación. La mayoría de las veces necesitamos realizar varias operaciones en matrices, de ahí este artículo.

En este artículo, le mostraré varios métodos para manipular matrices en JavaScript [^^]

¿Qué son las matrices en JavaScript?

Antes de continuar, debe comprender qué significan realmente las matrices.

En JavaScript, una matriz es una variable que se usa para almacenar diferentes tipos de datos. Básicamente almacena diferentes elementos en una caja y luego se puede evaluar con la variable.

Declarando una matriz:

let myBox = []; // Initial Array declaration in JS

Las matrices pueden contener varios tipos de datos

let myBox = ['hello', 1, 2, 3, true, 'hi'];

Las matrices se pueden manipular utilizando varias acciones conocidas como métodos. Algunos de estos métodos nos permiten agregar, eliminar, modificar y hacer mucho más en las matrices.

Te estaría mostrando algunos en este artículo, vamos a rodar :)

NB: Usé las funciones de Arrow en esta publicación, si no sabe lo que esto significa, debería leer aquí. La función de flecha es una característica de ES6 .

Encadenar()

El método JavaScript toString()convierte una matriz en una cadena separada por una coma.

let colors = ['green', 'yellow', 'blue']; console.log(colors.toString()); // green,yellow,blue

unirse()

El join()método JavaScript combina todos los elementos de la matriz en una cadena.

Es similar al toString()método, pero aquí puede especificar el separador en lugar de la coma predeterminada.

let colors = ['green', 'yellow', 'blue']; console.log(colors.join('-')); // green-yellow-blue

concat

Este método combina dos matrices juntas o agrega más elementos a una matriz y luego devuelve una nueva matriz.

let firstNumbers = [1, 2, 3]; let secondNumbers = [4, 5, 6]; let merged = firstNumbers.concat(secondNumbers); console.log(merged); // [1, 2, 3, 4, 5, 6]

empujar()

Este método agrega elementos al final de una matriz y cambia la matriz original.

let browsers = ['chrome', 'firefox', 'edge']; browsers.push('safari', 'opera mini'); console.log(browsers); // ["chrome", "firefox", "edge", "safari", "opera mini"]

popular()

Este método elimina el último elemento de una matriz y lo devuelve .

let browsers = ['chrome', 'firefox', 'edge']; browsers.pop(); // "edge" console.log(browsers); // ["chrome", "firefox"]

cambio()

Este método elimina el primer elemento de una matriz y lo devuelve .

let browsers = ['chrome', 'firefox', 'edge']; browsers.shift(); // "chrome" console.log(browsers); // ["firefox", "edge"]

unshift ()

Este método agrega un elemento (s) al comienzo de una matriz y cambia la matriz original.

let browsers = ['chrome', 'firefox', 'edge']; browsers.unshift('safari'); console.log(browsers); // ["safari", "chrome", "firefox", "edge"]
También puede agregar varios elementos a la vez

empalme()

EstaEl método cambia una matriz, agregando, quitando e insertando elementos.

La sintaxis es:

array.splice(index[, deleteCount, element1, ..., elementN])
  • Indexaquí está el punto de partida para eliminar elementos en la matriz
  • deleteCountes el número de elementos que se eliminarán de ese índice
  • element1, …, elementNes el (los) elemento (s) que se agregarán

Eliminar elementos

después de ejecutar splice () , devuelve la matriz con los elementos eliminados y la elimina de la matriz original. 
let colors = ['green', 'yellow', 'blue', 'purple']; colors.splice(0, 3); console.log(colors); // ["purple"] // deletes ["green", "yellow", "blue"]
NB : deleteCount no incluye el último índice del rango.

Si no se declara el segundo parámetro, todos los elementos a partir del índice dado se eliminarán de la matriz:

let colors = ['green', 'yellow', 'blue', 'purple']; colors.splice(3); console.log(colors); // ["green", "yellow", "blue"] // deletes ['purple']

En el siguiente ejemplo, eliminaremos 3 elementos de la matriz y los reemplazaremos con más elementos:

let schedule = ['I', 'have', 'a', 'meeting', 'tommorrow']; // removes 4 first elements and replace them with another schedule.splice(0, 4, 'we', 'are', 'going', 'to', 'swim'); console.log(schedule); // ["we", "are", "going", "to", "swim", "tommorrow"]

Agregar elementos

Para agregar elementos, debemos establecer el deleteCounten cero

let schedule = ['I', 'have', 'a', 'meeting', 'with']; // adds 3 new elements to the array schedule.splice(5, 0, 'some', 'clients', 'tommorrow'); console.log(schedule); // ["I", "have", "a", "meeting", "with", "some", "clients", "tommorrow"]

rebanada()

Este método es similar splice()pero muy diferente. Devuelve subarreglos en lugar de subcadenas.

Este método copia una parte determinada de una matriz y devuelve esa parte copiada como una nueva matriz. No cambia la matriz original.

La sintaxis es:

array.slice(start, end)

Aquí tienes un ejemplo básico:

let numbers = [1, 2, 3, 4] numbers.slice(0, 3) // returns [1, 2, 3] console.log(numbers) // returns the original array

La mejor forma de utilizarlo slice()es asignarlo a una nueva variable.

let message = 'congratulations' const abbrv = message.slice(0, 7) + 's!'; console.log(abbrv) // returns "congrats!"

división()

Este método se utiliza para cadenas . Divide una cadena en subcadenas y las devuelve como una matriz.

Here’s the syntax:string.split(separator, limit);

  • The separator here defines how to split a string either by a comma.
  • The limit determines the number of splits to be carried out
let firstName = 'Bolaji'; // return the string as an array firstName.split() // ["Bolaji"]

another example:

let firstName = 'hello, my name is bolaji, I am a dev.'; firstName.split(',', 2); // ["hello", " my name is bolaji"]
NB: If we declare an empty array, like this  firstName.split(''); then each item in the string will be divided as substrings: 
let firstName = 'Bolaji'; firstName.split('') // ["B", "o", "l", "a", "j", "i"]

indexOf()

This method looks for an item in an array and returns the index where it was found else it returns -1

let fruits = ['apple', 'orange', false, 3] fruits.indexOf('orange'); // returns 1 fruits.indexOf(3); // returns 3 friuts.indexOf(null); // returns -1 (not found)

lastIndexOf()

This method works the same way indexOf() does except that it works from right to left. It returns the last index where the item was found

let fruits = ['apple', 'orange', false, 3, 'apple'] fruits.lastIndexOf('apple'); // returns 4

filter()

This method creates a new array if the items of an array pass a certain condition.

The syntax is:

let results = array.filter(function(item, index, array) { // returns true if the item passes the filter });

Example:

Checks users from Nigeria

const countryCode = ['+234', '+144', '+233', '+234']; const nigerian = countryCode.filter( code => code === '+234'); console.log(nigerian); // ["+234", "+234"]

map()

This method creates a new array by manipulating the values in an array.

Example:

Displays usernames on a page. (Basic friend list display)

const userNames = ['tina', 'danny', 'mark', 'bolaji']; const display = userNames.map(item => { return '
  • ' + item + '
    • '; }) const render = '
    
      
     ' + display.join('') + '
    
    '; document.write(render);

    another example:

    // adds dollar sign to numbers const numbers = [10, 3, 4, 6]; const dollars = numbers.map( number => '$' + number); console.log(dollars); // ['$10', '$3', '$4', '$6'];

    reduce()

    This method is good for calculating totals.

    reduce() is used to calculate a single value based on an array.

    let value = array.reduce(function(previousValue, item, index, array) { // ... }, initial);

    example:

    To loop through an array and sum all numbers in the array up, we can use the for of loop. 
    const numbers = [100, 300, 500, 70]; let sum = 0; for (let n of numbers) { sum += n; } console.log(sum);

    Here’s how to do same with reduce()

    const numbers = [100, 300, 500, 70]; const sum = numbers.reduce((accummulator, value) => accummulator + value , 0); console.log(sum); // 970
    If you omit the initial value, the total will by default start from the first item in the array. 
    const numbers = [100, 300, 500, 70]; const sum = numbers.reduce((accummulator, value) => accummulator + value); console.log(sum); // still returns 970

    The snippet below shows how the reduce() method works with all four arguments.

    source: MDN Docs

    More insights into the reduce() method and various ways of using it can be found here and here.

    forEach()

    This method is good for iterating through an array.

    It applies a function on all items in an array

    const colors = ['green', 'yellow', 'blue']; colors.forEach((item, index) => console.log(index, item)); // returns the index and the every item in the array // 0 "green" // 1 "yellow" // 2 "blue"

    iteration can be done without passing the index argument

    const colors = ['green', 'yellow', 'blue']; colors.forEach((item) => console.log(item)); // returns every item in the array // "green" // "yellow" // "blue"

    every()

    This method checks if all items in an array pass the specified condition and returntrue if passed, else false.

    check if all numbers are positive 
    const numbers = [1, -1, 2, 3]; let allPositive = numbers.every((value) => { return value >= 0; }) console.log(allPositive); // would return false

    some()

    This method checks if an item (one or more) in an array pass the specified condition and return true if passed, else false.

    checks if at least one number is positive 
    const numbers = [1, -1, 2, 3]; let atLeastOnePositive = numbers.some((value) => { return value >= 0; }) console.log(atLeastOnePositive); // would return true

    includes()

    This method checks if an array contains a certain item. It is similar to .some(), but instead of looking for a specific condition to pass, it checks if the array contains a specific item.

    let users = ['paddy', 'zaddy', 'faddy', 'baddy']; users.includes('baddy'); // returns true

    If the item is not found, it returns false

    There are more array methods, this is just a few of them. Also, there are tons of other actions that can be performed on arrays, try checking MDN docs herefor deeper insights.

    Summary

    • toString() converts an array to a string separated by a comma.
    • join() combines all array elements into a string.
    • concat combines two arrays together or add more items to an array and then return a new array.
    • push() adds item(s) to the end of an array and changes the original array.
    • pop() removes the last item of an array and returns it
    • shift() removes the first item of an array and returns it
    • unshift() adds an item(s) to the beginning of an array and changes the original array.
    • splice() changes an array, by adding, removing and inserting elements.
    • slice() copiesa given part of an array and returns that copied part as a new array. It does not change the original array.
    • split() divides a string into substrings and returns them as an array.
    • indexOf() looks for an item in an array and returns the index where it was found else it returns -1
    • lastIndexOf() looks for an item from right to left and returns the last index where the item was found.
    • filter() creates a new array if the items of an array pass a certain condition.
    • map() creates a new array by manipulating the values in an array.
    • reduce() calculates a single value based on an array.
    • forEach() iterates through an array, it applies a function on all items in an array
    • every() checks if all items in an array pass the specified condition and return true if passed, else false.
    • some() checks if an item (one or more) in an array pass the specified condition and return true if passed, else false.
    • includes() checks if an array contains a certain item.

    Let’s wrap it here; Arrays are powerful and using methods to manipulate them creates the Algorithms real-world applications use.

    Let's do a create a small function, one that converts a post title into a urlSlug.

    URL slug is the exact address of a specific page or post on your site.

    When you write an article on Freecodecamp Newsor any other writing platform, your post title is automatically converted to a slug with white spaces removed, characters turned to lowercase and each word in the title separated by a hyphen.

    Here’s a basic function that does that using some of the methods we learnt just now.

    const url = '//bolajiayodeji.com/' const urlSlug = (postTitle) => { let postUrl = postTitle.toLowerCase().split(' '); let postSlug = `${url}` + postUrl.join('-'); return postSlug; } let postTitle = 'Introduction to Chrome Lighthouse' console.log(urlSlug(postTitle)); // //bolajiayodeji.com/introduction-to-chrome-lighthouse

    in postUrl, we convert the string to lowercase then we use the split()method to convert the string into substrings and returns it in an array

    ["introduction", "to", "chrome", "lighthouse"]

    in post slug we join the returned array with a hyphen and then concatenate it to the category string and main url.

    let postSlug = `${url}` + postUrl.join('-'); postUrl.join('-') // introduction-to-chrome-lighthouse

    That’s it, pretty simple, right? :)

    If you’re just getting started with JavaScript, you should check this repository here, I’m compiling a list of basic JavaScript snippets ranging from

    • Arrays
    • Control flow
    • Functions
    • Objects
    • Operators

    Don’t forget to Star and share! :)

    PS: This article was first published on my blog here