PHP Arrays Tutorial

There are many benefits of using arrays. The great thing about arrays is that you can keep together a collection of variables that are to be used in combination, which should be connected. An example of the usage would be for a shopping cart system. You could make an array that holds all products that are added to the shopping cart. We could make the sub-variables of the array be ids of the products, and the values be the amount of times the product is added to the shopping cart. E.g.:

$shopping_cart = array(9 => 1, 5 => 1, 23 => 4);

This array would then illustrate a shopping cart with the products with the ids 9 (2x), 5 (1x), 23 (4x). If we would want to add another product to the shopping cart we could just do that by ading it to the array, like this:

$product_id = 10;
$amount = 1;
$shopping_cart[$product_id] = $amount;

It will add the product with the id $product_id (=10 in this example) to the shopping cart, and set the amount equal to $amount (=1 in this example). If it's already inside of the shopping cart, it will replace the amount of that product (=value of the sub-variable for that product id).

To remove a product from the shopping cart, we'd just unset the sub-variable out of the array:

unset($shopping_cart[$product_id]);

To check whether a certain product is inside of the shopping cart, we'd just use an if loop to check whether the sub-variable $product_id is set inside of the array $shopping_cart:

if(isset($shopping_cart[$product_id]) {

}

Another great benefit of having these products in one array is that we can just loop through them using a foreach loop. We'll see that in the next post.

The foreach loop is a very useful loop with which we can easily loop through an array. It works like this:

foreach($array AS $key => $value) {
executable code
}

where $array is the array variable. The loop will run the executable code (between accolades) for each sub-variable of the array and put the sub-variable name inside $key and the value inside $value. If we use this for our shopping cart array, we could enlist all products inside of the shopping cart this way:

foreach($shopping_cart AS $id => $amount) {
echo "<p>#{$id} ({$amount}x) </p>";
}

which will list all ids of the products and their amounts.

It's also possible to create multi-dimensional arrays - creating an array inside of an array. For example:

$locations = array (
"USA" => array("New York", "Alabama"),
"The Netherlands" => array("Amsterdam", "Utrecht")
);

and to access a sub-variable:

$locations['USA']; //accesses an array
$locations['USA'][0]; //accesses the first sub-variable of that array (containing "New York")

Accessing sub-variables of a multi-dimensional array works just the same way as for normal arrays. Only now you can access a sub-variable of a sub-variable:

You can create mult-dimensional arrays at any level. Make them as large and complicated as you like, but it's never good to make your code unecessarily complicated. So try to always keep it as simple as possible (also for the readability).

Here's a couple of useful functions that can come handy when working with arrays:

count($array)
Counts the amount of sub-variables inside of array $array.

Example:

$array = array(10, 4, 21);
$result = count($array); //returns 3

explode($str1, $str2)
Forms an array out of the string $str2, exploding the string by the character/string $str1.

Example:

$str1 = ","; //a comma
$str2 = "keyword1,keyword2,keyword3";
$result = explode($str1, $str2); //creates the array: array("keyword1", "keyword2", "keyword3")

implode($str, $array)
Forms a string out of the array $array, merging all values of the array together to one string using $str1 to merge the values with eachother ( seperate ).

Example:

$str = " and ";
$array = array("item1", "item2", "item3");
$result = implode($str, $array); //creates the string: "item1 and item2 and item3"

strsplit($str1[, $str2])
Converts the string $str into an array with $str2 being the maximum length of the chunk ( if any ).

Example:

$str1 = "abc";
$result = str_split($str1); //creates the array: array("a", "b", "c")