PHP Arrays

What are Arrays?

Arrays are a collection of elements that are stored in a single variable. PHP supports several types of arrays that allow you to store multiple values in an organized way.

Types of Arrays in PHP

PHP supports three main types of arrays, each serving a different purpose.

Indexed Arrays: Arrays with numeric keys.
Associative Arrays: Arrays with named keys (key-value pairs).
Multidimensional Arrays: Arrays containing other arrays.

1. Indexed Arrays

This is the simplest type of array. It’s an ordered list where each value is identified by a numeric index, which starts at 0.

Creating Indexed Arrays: Syntax

You can use the modern short array syntax [] (recommended) or the older array() constructor.

// Method 1: Using array() function
$fruits = array("apple", "banana", "orange");

// Method 2: Using short array syntax (PHP 5.4+)
$fruits = ["apple", "banana", "orange"];

// Method 3: Manual assignment
$fruits[0] = "apple";
$fruits[1] = "banana";
$fruits[2] = "orange";

Accessing Elements:

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

<?php
$colors = ["Red", "Green", "Blue"];

// Remember, the index starts at 0!
echo $colors[0]; // Outputs: Red
echo "<br>";
echo $colors[2]; // Outputs: Blue

// You can also modify an element
$colors[1] = "Yellow";
echo "<br>";
echo $colors[1]; // Outputs: Yellow

// To add a new element to the end of the array
$colors[] = "Purple";
// The $colors array is now ["Red", "Yellow", "Blue", "Purple"]
?>

2. Associative Arrays

Associative arrays use named keys instead of numeric indices.
They are the foundation of how PHP handles form data ($_POST, $_GET) and much more.
Instead of using numeric indexes, you assign a custom key (a string) to each value.

Creating Associative Arrays: Syntax

The syntax uses => to associate a key with a value.

// Method 1: Using array() function
$person = array(
    "name" => "John Doe",
    "age" => 30,
    "city" => "New York"
);

// Method 2: Using short array syntax (PHP 5.4+)
$person = [
    "name" => "John Doe",
    "age" => 30,
    "city" => "New York"
];

// Method 3: Manual assignment
$person["name"] = "John Doe";
$person["age"] = 30;
$person["city"] = "New York";

Accessing Associative Array Elements

You access elements using their unique string keys.

<?php
$user = [
    "firstName" => "John",
    "lastName"  => "Doe",
    "email"     => "john.doe@example.com"
];

echo "User's email is: " . $user["email"]; // Outputs: User's email is: john.doe@example.com

// Modifying a value
$user["email"] = "j.doe@newdomain.com";

// Adding a new key-value pair
$user["city"] = "New York";
?>

Best Practices for Arrays

// Good practice: Type hinting
function processNumbers(array $numbers): array {
    return array_map(function($n) {
        return $n * 2;
    }, $numbers);
}

// Good practice: Check if key exists
if (isset($person["email"])) {
    echo $person["email"];
} else {
    echo "Email not provided";
}

3. Multidimensional Arrays

A multidimensional array is an array that contains one or more other arrays. This is perfect for representing complex data structures like a list of products where each product has its own properties, or rows of data from a database table.

Creating Multidimensional Arrays: Syntax

// 2D Array
$students = [
    ["John", 85, "Math"],
    ["Jane", 92, "Science"],
    ["Bob", 78, "History"]
];

// Associative multidimensional array
$products = [
    "laptop" => [
        "brand" => "Dell",
        "price" => 800,
        "specs" => ["RAM" => "8GB", "Storage" => "256GB SSD"]
    ],
    "phone" => [
        "brand" => "iPhone",
        "price" => 999,
        "specs" => ["RAM" => "6GB", "Storage" => "128GB"]
    ]
];

Accessing Elements:

// Accessing 2D array
echo $students[0][0]; // Output: John
echo $students[1][2]; // Output: Science

// Accessing associative multidimensional array
echo $products["laptop"]["brand"]; // Output: Dell
echo $products["phone"]["specs"]["RAM"]; // Output: 6GB

Common Array Operations

Adding Elements

$fruits = ["apple", "banana"];

// Add to end
$fruits[] = "orange";
array_push($fruits, "grape", "mango");

// Add to beginning
array_unshift($fruits, "strawberry");

// Add at specific index (associative)
$fruits["tropical"] = "pineapple";

Removing Elements

$fruits = ["apple", "banana", "orange", "grape"];

// Remove last element
$lastFruit = array_pop($fruits);

// Remove first element
$firstFruit = array_shift($fruits);

// Remove specific element by key
unset($fruits[1]);

// Remove specific value
$key = array_search("orange", $fruits);
if ($key !== false) {
    unset($fruits[$key]);
}

Looping Through Arrays

For Loop (Indexed Arrays):

$numbers = [1, 2, 3, 4, 5];

for ($i = 0; $i < count($numbers); $i++) {
    echo $numbers[$i] . " ";
}

Foreach Loop:

The most common task you’ll perform with an array is to loop through it and do something with each element. The foreach loop is designed specifically for this.

<?php
// Looping through an indexed array
$colors = ["Red", "Green", "Blue"];

echo "<ul>";
foreach ($colors as $color) {
    echo "<li>" . $color . "</li>";
}
echo "</ul>";


// Looping through an associative array to get both key and value
$user = [
    "First Name" => "John",
    "Last Name"  => "Doe",
    "Email"      => "john.doe@example.com"
];

echo "<h3>User Details</h3>";
foreach ($user as $key => $value) {
    echo "<strong>" . $key . ":</strong> " . $value . "<br>";
}
?>

While Loop:

$fruits = ["apple", "banana", "orange"];
$i = 0;

while ($i < count($fruits)) {
    echo $fruits[$i] . " ";
    $i++;
}

Useful Array Functions

Array Information

$fruits = ["apple", "banana", "orange"];

// Get array length
$length = count($fruits); // 3

// Check if array is empty
$isEmpty = empty($fruits); // false

// Check if key exists
$keyExists = array_key_exists("name", $person); // true/false

// Check if value exists
$valueExists = in_array("apple", $fruits); // true

Array Manipulation

$numbers = [3, 1, 4, 1, 5, 9];

// Sort array
sort($numbers); // [1, 1, 3, 4, 5, 9]

// Reverse array
$reversed = array_reverse($numbers);

// Get unique values
$unique = array_unique($numbers);

// Filter array
$evenNumbers = array_filter($numbers, function($n) {
    return $n % 2 == 0;
});

// Map array (transform each element)
$doubled = array_map(function($n) {
    return $n * 2;
}, $numbers);

Array Merging and Splitting

$array1 = ["a", "b", "c"];
$array2 = ["d", "e", "f"];

// Merge arrays
$merged = array_merge($array1, $array2);

// Split array into chunks
$chunks = array_chunk($merged, 2);

// Extract slice of array
$slice = array_slice($merged, 1, 3);

Practical Examples

Example 1: Student Grade Management

$students = [
    "Alice" => ["Math" => 85, "Science" => 92, "English" => 78],
    "Bob" => ["Math" => 76, "Science" => 84, "English" => 88],
    "Charlie" => ["Math" => 93, "Science" => 89, "English" => 95]
];

// Calculate average grade for each student
foreach ($students as $name => $grades) {
    $average = array_sum($grades) / count($grades);
    echo "$name's average: " . round($average, 2) . "<br>";
}

// Find highest grade in Math
$mathGrades = array_column($students, 'Math');
$highestMath = max($mathGrades);
echo "Highest Math grade: $highestMath<br>";

Example 2: Shopping Cart

$cart = [
    "laptop" => ["price" => 800, "quantity" => 1],
    "mouse" => ["price" => 25, "quantity" => 2],
    "keyboard" => ["price" => 50, "quantity" => 1]
];

// Calculate total cost
$total = 0;
foreach ($cart as $item => $details) {
    $itemTotal = $details["price"] * $details["quantity"];
    $total += $itemTotal;
    echo "$item: $" . $itemTotal . "<br>";
}

echo "Total: $" . $total . "<br>";

Example 3: Data Processing

$employees = [
    ["name" => "John", "department" => "IT", "salary" => 50000],
    ["name" => "Jane", "department" => "HR", "salary" => 45000],
    ["name" => "Bob", "department" => "IT", "salary" => 55000],
    ["name" => "Alice", "department" => "Finance", "salary" => 48000]
];

// Group employees by department
$byDepartment = [];
foreach ($employees as $employee) {
    $dept = $employee["department"];
    $byDepartment[$dept][] = $employee;
}

// Calculate average salary by department
foreach ($byDepartment as $dept => $deptEmployees) {
    $salaries = array_column($deptEmployees, 'salary');
    $avgSalary = array_sum($salaries) / count($salaries);
    echo "$dept average salary: $" . number_format($avgSalary) . "<br>";
}