Learn PHP Arrays

PHP Arrays

An array is a special variable, which can hold more than one value at a time.
An array stores multiple values in one single variable:

Example

$cars = array("Volvo", "BMW", "Toyota");

What is an Array?

In PHP, there are three types of arrays:

• Indexed arrays - Arrays with a numeric index
• Associative arrays - Arrays with named keys
• Multidimensional arrays - Arrays containing one or more arrays

Working With Arrays

In PHP, there are several pre-defined arrays functions, which can be used to work with arrays.

• Create Arrays
• Access Arrays
• Update Arrays
• Add Array Items
• Remove Array Items
• Sort Arrays

Array Items

Array items can be of any data type.
The most common are strings and numbers (int, float), but array items can also be objects, functions or even arrays.
You can have different data types in the same array.

Example

Array items of four different data types:

$myArr = array("Volvo", 15, ["apples", "bananas"], myFunction);

Array Functions

The real strength of PHP arrays are the built-in array functions, like the count() function for counting array items:

Example

            $cars = array("Volvo", "BMW", "Toyota");
            echo count($cars);

PHP Indexed Arrays

An indexed array is an array that uses numerical keys.
The keys are assigned automatically.

Example

Create and display an indexed array:

            $cars = array("Volvo", "BMW", "Toyota");
            var_dump($cars);

Access Indexed Arrays

You access an array element by referring to its index number inside square brackets [].

Example

            $cars = array("Volvo", "BMW", "Toyota");
            echo $cars[0];

Access Indexed Arrays

You access an array element by referring to its index number inside square brackets [].

Example

        $cars = array("Volvo", "BMW", "Toyota");
        echo $cars[0];

Change Value

To change the value of a specific indexed array, refer to the index number, and use the assignment operator (=)

Example

Change the value of the second item:

        $cars = array("Volvo", "BMW", "Toyota");
        $cars[1] = "Ford";
        var_dump($cars);

Loop Through an Indexed Array

To loop through and print all the values of an indexed array, you could use a foreach loop, like this:

Example

Display all array items:

        $cars = array("Volvo", "BMW", "Toyota");
        foreach ($cars as $x) {
        echo "$x <br>";
        }

Index Number

In PHP, index numbers typically refer to the position of an element within an array.
Each element in an array has an index number that indicates its position, starting from 0 for the first element.
New items get the next index number, meaning one higher than the highest existing index.
So if you have an array like this:

        $cars[0] = "Volvo";
        $cars[1] = "BMW";
        $cars[2] = "Toyota";

And if you use the array_push() function to add a new item, the new item will get the index 3:

Example

        array_push($cars, "Ford");
        var_dump($cars);

But if you have an array with random index numbers, like this:

Example

        $cars[5] = "Volvo";
        $cars[7] = "BMW";
        $cars[14] = "Toyota";

And if you use the array_push() function to add a new item, what will be the index number of the new item?

Example

        array_push($cars, "Ford");
        var_dump($cars);

PHP Associative Arrays

Associative arrays are arrays that use named keys that you assign to them.

Example

        $car = array("brand"=>"Ford", "model"=>"Mustang", "year"=>1964);
        var_dump($car);

Access Associative Arrays

To access an array item you can refer to the key name.

Example

Display the model of the car:

        $car = array("brand"=>"Ford", "model"=>"Mustang", "year"=>1964);
        echo $car["model"];

Change Value

To change the value of an array item, use the key name:

Example

Change the year item:

          $car = array("brand"=>"Ford", "model"=>"Mustang", "year"=>1964);
          $car["year"] = 2024;
          var_dump($car);

Loop Through an Associative Array

You can loop through each key/value pair in an associative array with the foreach loop

Example

Display all array items, keys and values:

        $car = array("brand"=>"Ford", "model"=>"Mustang", "year"=>1964);

        foreach ($car as $x => $y) {
          echo "$x: $y <br>";
        }

PHP Create Arrays

You can create arrays by using the array() function:

Example

Create an array:

$cars = array("Volvo", "BMW", "Toyota");

You can also use a shorter syntax by using the [] brackets:

Example

$cars = ["Volvo", "BMW", "Toyota"];

Multiple Lines

You can also create an array with multiple lines:

Example

      $cars = [
        "Volvo",
        "BMW",
        "Toyota"
      ];

Trailing Comma

PHP 5 allows you to end an array declaration with a trailing comma:

Example

     $cars = [
        "Volvo",
        "BMW",
        "Toyota",
      ];

Array Keys

When creating indexed arrays the keys are given automatically, starting at 0 and increased by 1 for each item, so the array above could also be created with keys:

Example

      $cars = [
        0 => "Volvo",
        1 => "BMW",
        2 =>"Toyota"
      ];

As you can see, indexed arrays are the same as associative arrays, but associative arrays have names instead of numbers:

Example

     $myCar = [
        "brand" => "Ford",
        "model" => "Mustang",
        "year" => 1964
      ];

Declare Empty Array

You can declare an empty array first, and add items to it later:

Example

        $cars = [];
        $cars[0] = "Volvo";
        $cars[1] = "BMW";
        $cars[2] = "Toyota";

The same goes for associative arrays, you can declare the array first, and then add items to it:

Example

        $myCar = [];
        $myCar["brand"] = "Ford";
        $myCar["model"] = "Mustang";
        $myCar["year"] = 1964;

Mixing Array Keys

You can have arrays with both indexed and named keys:

Example

        $myArr = [];
        $myArr[0] = "apples";
        $myArr[1] = "bananas";
        $myArr["fruit"] = "cherries";

PHP Access Arrays

Access Array Item

To access an array item, you can refer to the index number for indexed arrays, and the key name for associative arrays.

Example

Access an item by referring to its index number:

        $cars = array("Volvo", "BMW", "Toyota");
        echo $cars[2];

Note: The first item has index 0.

To access items from an associative array, use the key name:

Example

Access an item by referring to its key name:

          $cars = array("brand" => "Ford", "model" => "Mustang", "year" => 1964);
          echo $cars["year"];

Double or Single Quotes

In PHP, the keys of an associative array are always strings. If you don't use double quotes, the key will be quoted as a string

Example

You can use both double and single quotes when accessing an array:

          echo $cars["model"];
          echo $cars['model'];

Excecute a Function Item

Array items can be of any data type, including function.
To execute such a function, use the index number followed by parentheses ():

Example

Execute a function item:

       function myFunction() {
          echo "I come from a function!";
        }
        
        $myArr = array("Volvo", 15, myFunction);
        
        $myArr[2]();

Use the key name when the function is an item in a associative array:

Example

Execute function by referring to the key name:

       function myFunction() {
          echo "I come from a function!";
        }
        
        $myArr = array("car" => "Volvo", "age" => 15, "message" => myFunction);
        
        $myArr["message"]();

Loop Through an Associative Array

To loop through and print all the values of an associative array, you can use a foreach loop, like this:

Example

Display all array items, keys and values:

         $car = array("brand"=>"Ford", "model"=>"Mustang", "year"=>1964);

          foreach ($car as $x => $y) {
            echo "$x: $y <br>";
          }

Loop Through an Indexed Array

To loop through and print all the values of an indexed array, you can use a foreach loop, like this:

Example

Display all array items:

         $cars = array("Volvo", "BMW", "Toyota");
          foreach ($cars as $x) {
            echo "$x <br>";
          }

PHP Update Array Items

You can also change the value of an indexed array element by using the array key and its new value :

Example

Change the second array item from "BMW" to "Ford":

            $cars = array("Volvo", "BMW", "Toyota");
            $cars[1] = "Ford";

Note: The first item has index 0.

Update Array Items in a Foreach Loop

There are different techniques to use when changing item values in a foreach loop.

One way is to insert the & character in the assignment to assign the item value by reference, and thereby making sure that any changes done with the array item inside the loop will be done to the original array:

Example

Change ALL item values to "Ford":

           $cars = array("Volvo", "BMW", "Toyota");
            foreach ($cars as &$x) {
              $x = "Ford";
            }
            unset($x);
            var_dump($cars);

Note: Remember to add the unset() function after the loop.
Without the unset($x) function, the$x variable will remain as a reference to the last array item.
To demonstrate this, see what happens when we change the value of $x after the foreach loop:

Example

Demonstrate the consequence of forgetting theunset() function:

          $cars = array("Volvo", "BMW", "Toyota");
            foreach ($cars as &$x) {
              $x = "Ford";
            }
            
            $x = "ice cream";
            
            var_dump($cars);

PHP Add Array Items

To add items to an existing array, you can use the bracket [] syntax.

Example

Add one more item to the fruits array:

            $fruits = array("Apple", "Banana", "Cherry");
            $fruits[] = "Orange";

Associative Arrays

To add items to an associative array, or key/value array, use brackets [] for the key, and assign value with the = operator.

Example

Add one item to the car array:

            $cars = array("brand" => "Ford", "model" => "Mustang");
            $cars["color"] = "Red";

Add Multiple Array Items

To add multiple items to an existing array, use the array_push() function.

Example

Add three item to the fruits array:

            $fruits = array("Apple", "Banana", "Cherry");
            array_push($fruits, "Orange", "Kiwi", "Lemon");

Add Multiple Items to Associative Arrays

To add multiple items to an existing array, you can use the += operator.

Example

Add two items to the cars array:

            $cars = array("brand" => "Ford", "model" => "Mustang");
            $cars += ["color" => "red", "year" => 1964];

PHP Delete Array Items

Remove Array Item

To remove an existing item from an array, you can use the array_splice() function.
With the array_splice() function you specify the index (where to start) and how many items you want to delete.

Example

Remove the second item:

            $cars = array("Volvo", "BMW", "Toyota");
            array_splice($cars, 1, 1);

After the deletion, the array gets reindexed automtically, starting at index 0.

Using the unset Function

You can also use the unset() function to delete existing array items.

Note: The unset() function does not re-arrange the indexes, meaning that after deletion the array will no longer contain the missing indexes.

Example

Remove the second item:

            $cars = array("Volvo", "BMW", "Toyota");
            unset($cars[1]);

Remove Multiple Array Items

You can remove multiple array items by using the array_splice() function.

Example

Remove 2 items, starting a the second item (index 1):

            $cars = array("Volvo", "BMW", "Toyota");
            array_splice($cars, 1, 2);

The unset() function takes a unlimited number of arguments, and can therefor be used to delete multiple array items:

Example

            $cars = array("Volvo", "BMW", "Toyota");
            unset($cars[0], $cars[1]);

Remove Item From an Associative Array

To remove items from an associative array, you can use the unset() function. Specify the key of the item you want to delete.

Example

Remove the "model":

            $cars = array("brand" => "Ford", "model" => "Mustang", "year" => 1964);
            unset($cars["model"]);

Using the array_diff Function

You can also use the array_diff() function to remove items from an associative array.
This function returns a new array, without the specified items.

Example

Create a new array, without "Mustang" and "1964":

            $cars = array("brand" => "Ford", "model" => "Mustang", "year" => 1964);
            $newarray = array_diff($cars, ["Mustang", 1964]);

Note: The array_diff() function takes values as parameters, and not keys.

Remove the Last Item

The array_pop() function removes the last item of an array.

Example

Remove the last item:

            $cars = array("Volvo", "BMW", "Toyota");
            array_pop($cars);

Remove the First Item

The array_shift() function removes the first item of an array.

Example

            $cars = array("Volvo", "BMW", "Toyota");
            array_shift($cars);

PHP Array Functions

PHP has a set of built-in functions that you can use on arrays.