arrays

Arrays#

Arrays
Array Declaration
Manipulate Arrays
Loops

Arrays : #

Onedimensional Arrays: ⏬#

Objects allow you to store keyed collections of values. That’s fine.

But quite often we find that we need an ordered collection, where we have a 1st, a 2nd, a 3rd element and so on.
For example, we need that to store a list of something: users, goods, HTML elements etc.

It is not convenient to use an object here, because it provides no methods to manage the order of elements. We can’t insert a new property “between” the existing ones. Objects are just not meant for such use.

There exists a special data structure named Array, to store ordered collections.

What is ARRAYS means :#

Arrays : Are single variables used to store ordered and different kind of elements(collections).

SO : the array variable can hold more than one value at a time.

Array Declaration : #

We have two ways to create(declare) empty array

 1- let arr = new Array();
  // return arr = []
 2- let arr = [];

Almost all the time, the second syntax is used. and We can supply initial elements in the brackets:

let numbers = new Array(1, 2, 3);
console.log(numbers); // [1, 2, 3]

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

Array elements are numbered, starting with zero. [This thing called indexing]#

We can get an element by its number in square brackets:

                  0       1         2
  let colors = ['Red', 'Yellow', 'Green'];

  console.log( colors[0] ); // Red
  console.log( colors[1] ); // Yellow
  console.log( colors[2] ); // Green

We can replace an element:

                               0         1       2
 colors[2] = 'Blue'; // now ['Red', 'Yellow', 'Blue']

…Or add a new one to the array:

                               0        1       2       3
 colors[3] = 'Pink'; // now ['Red', 'Yellow', 'Blue', 'Pink']

The total count of the elements in the array is its length:

console.log(colors.length);
// 4

The Array can store elements of any type.#

For Example:

// mix of values
let arr = [
  "Apple",
  { name: "Fatma" },
  true,
  function () {
    console.log("hello");
  },
];

// get the object at index 1 and then show its name
console.log(arr[1].name); // Fatma

// get the function at index 3 and run it
arr[3](); // hello

Manipulate Arrays : #

arrays are mutable So array state can be modified after it is created. let's see the following example:

let arr = ["Fatma", "Ala'a"];
arr[2] = "Sama";
arr; // ["Fatma", "Ala'a", "Sama"]

Multidimensional Arrays : ⏬#

Arrays can have items that are also arrays. We can use it for multidimensional arrays, for example to store matrices:

let activities = [
  /*0*/ /*1*/ /*0*/ ["Working ", 9],
  /*1*/ ["Eating  ", 2],
  /*2*/ ["Commute ", 2],
  /*3*/ ["Sleeping", 7],
];

console.log(activities[1]); //  ['Eating  ', 2]
console.log(activities[3]); //  ['Sleeping', 7]

console.log(activities[1][1]); // 2
console.log(activities[0][0]); // Working
console.log(activities[3][0]); // Sleeping

activities[4] = ["Study   ", 10];

// now
activities = [
  ["Working ", 9][("Eating  ", 2)][("Commute ", 2)][("Sleeping", 7)][
    ("Study  ", 10)
  ],
];