Arrays

• Arrays are also a collection of variables. They used for lists of similar variables (i.e. a bunch of numbers, or images).
• Arrays are indexed. Supplying the index (typically a number) to the array will return the variable at that index.
• Array indexes start at zero (0), and progress upwards
• To get an item out of the array, use the square brackets and the index

Array Metaphor

• You could think of arrays as a filing cabinet…
• You can only put one item into each box, and you label them so you can find them with ease.
• The labels are the indexes of the cabinet / array

Making an Array

	var myArray = [1,2,3,4];

	var myArray = [];

Getting a value out of an array

Write the square brackets, and inside the index you want.

	var myArray = [5,4,3,2,1];
	myArray[0]; // 5
	myArray[2]; // 3
	myArray[3]; // 2

Modifying the array

• Write the square brackets to get to what is stored in that index of the array
• Works just like a variable

	myArray[0] = 5;
	myArray[3] = 39;

Useful array properties and methods

• length: returns the number of elements in the array
• push(something): adds an element at index zero, pushes all others back
• pop(): takes a variable off the top of the array and returns it
• shift(something): adds an element at the very end of the array
• unshift(): takes a variable off the bottom of the array
• sort(): will sort the variables numerically or alphabetically
• splice(index, number): removes and returns (number) of elements from the array, starting at (index)
• toString(): Like number.toString. This returns a string of every entry in the array

Some array examples

	var myArray = new Array("This", "array", "already", "has", "some", "content");
	console.log(myArray[0]);
	console.log(myArray[2]);
	console.log(myArray.toString());

Output This already This, array, already, has, some, content

	var myArray = new Array("This", "array", "already", "has", "some", "content");
	var firstWord = myArray.pop();
	console.log(firstWord);
	var lastWord = myArray.shift();
	console.log(lastWord);
	console.log("Length " + myArray.length);

Output This content Length: 4

Splitting strings

Its possible to make an array out of strings by splitting them

Example:

	var statement = "Some dogs have two teeth";
	var splitStatement = statement.split(" "); //split on the spaces

The data in splitStatement will be [ “some”, “dogs”, “have”, “two”, “teeth” ]

Yep, you can split on anything

	var source = "Dogs,cats,rats,mice";
	var split = source.split(","); // [ "Dogs", "cats", "rats", "mice" ]

	var source = "Dogs,cats,rats,mice";
	var split = source.split("rats,"); // [ “Dogs,cats,”,“mice” ];

‘Iterating’ through an array

	var myArray = [ 2, 4, 6, 8, 10 ];
	for(var i = 0; i < myArray.length; i++) {
		var itemAtIndex = myArray[i];
		console.log(itemAtIndex);
	}

Summing up items in an array

	var sum = 0;
	var myArray = [ 2, 4, 6, 8, 10 ];
	for(var i = 0; i < myArray.length; i++) {
		var itemAtIndex = myArray[i];
		sum += itemAtIndex;
	}

Searching Arrays

	var myArray = [ "Spock", "Kirk", "McCoy", "Luffy" ];
	var thingToLookFor = "Luffy";

	for(var i = 0; i < myArray.length; i++) {
		var itemAtIndex = myArray[i];
		if( itemAtIndex == thingToLookFor) {
			break;
		}
	}

Parallel Arrays

• Storing data associated with each other in two different arrays
• Data at the same index in each array are assumed to be related.
• Here one array stores names, while the other stores employment

var names = [ "Stan", "Lee", "Isolde" ];
var employment = [ "Janitor", "Cook", "Queen" ];

• In the example above, entry 0 in names is related to entry 0 in employment.
• So Stan is a Janitor, Lee is a cook, and Isolde is a Queen
• Can easily get all the data with a for loop

for( var i = 0; i < names.length; i++) {
	console.log( names[i] + " is a " + employment[i]);
}