PHP Array Operations

Arrays are fundamental data structures in PHP that allow you to store multiple values in a single variable. Understanding how to manipulate arrays effectively is crucial for PHP development. This guide covers the essential operations you'll need to work with arrays in PHP.

Introduction to PHP Array Operations

In PHP, arrays are incredibly versatile and can store values of different types together. The language provides numerous built-in functions and operators to create, modify, access, and process array data. Whether you're building a simple website or a complex application, mastering array operations will significantly enhance your PHP programming skills.

Creating Arrays

PHP offers multiple ways to create arrays:

Basic Array Creation

php

// Simple indexed array
$fruits = array("Apple", "Banana", "Orange");

// Using the short array syntax (PHP 5.4+)
$vegetables = ["Carrot", "Broccoli", "Spinach"];

// Output
echo '<pre>';
print_r($fruits);
echo '</pre>';

Output:

Array
(
    [0] => Apple
    [1] => Banana
    [2] => Orange
)

Associative Arrays

Associative arrays use named keys instead of numeric indices:

php

// Associative array
$person = array(
    "name" => "John Doe",
    "age" => 28,
    "email" => "[email protected]"
);

// Short syntax
$settings = [
    "theme" => "dark",
    "notifications" => true,
    "sidebar" => "left"
];

// Output
echo '<pre>';
print_r($person);
echo '</pre>';

Output:

Array
(
    [name] => John Doe
    [age] => 28
    [email] => [email protected]
)

Multidimensional Arrays

Arrays can contain other arrays, creating multidimensional structures:

php

// 2D array
$students = [
    ["name" => "Alice", "grade" => 85],
    ["name" => "Bob", "grade" => 92],
    ["name" => "Charlie", "grade" => 78]
];

// 3D array example
$classrooms = [
    "ClassA" => [
        "Alice" => ["Math" => 90, "Science" => 95],
        "Bob" => ["Math" => 85, "Science" => 80]
    ],
    "ClassB" => [
        "Charlie" => ["Math" => 75, "Science" => 85],
        "Dave" => ["Math" => 95, "Science" => 90]
    ]
];

// Output
echo '<pre>';
print_r($students);
echo '</pre>';

Output:

Array
(
    [0] => Array
        (
            [name] => Alice
            [grade] => 85
        )
    [1] => Array
        (
            [name] => Bob
            [grade] => 92
        )
    [2] => Array
        (
            [name] => Charlie
            [grade] => 78
        )
)

Array Access and Modification

Accessing Array Elements

php

$colors = ["red", "green", "blue", "yellow"];

// Access by index
echo $colors[0]; // Outputs: red

$user = ["name" => "Jane", "role" => "Admin"];

// Access by key
echo $user["role"]; // Outputs: Admin

// Accessing nested arrays
$data = [
    "products" => [
        ["id" => 1, "name" => "Laptop"],
        ["id" => 2, "name" => "Phone"]
    ]
];

echo $data["products"][1]["name"]; // Outputs: Phone

Adding Elements

php

$fruits = ["Apple", "Banana"];

// Add to the end
$fruits[] = "Orange";

// Add with specific key
$fruits[3] = "Mango";

// Add to associative array
$user = ["name" => "John"];
$user["email"] = "[email protected]";

// Output
echo '<pre>';
print_r($fruits);
print_r($user);
echo '</pre>';

Output:

Array
(
    [0] => Apple
    [1] => Banana
    [2] => Orange
    [3] => Mango
)
Array
(
    [name] => John
    [email] => [email protected]
)

Modifying Elements

php

$numbers = [10, 20, 30, 40];

// Change value
$numbers[2] = 35;

$settings = ["theme" => "light", "sidebar" => "left"];

// Update value
$settings["theme"] = "dark";

// Output
echo '<pre>';
print_r($numbers);
print_r($settings);
echo '</pre>';

Output:

Array
(
    [0] => 10
    [1] => 20
    [2] => 35
    [3] => 40
)
Array
(
    [theme] => dark
    [sidebar] => left
)

Removing Elements

php

$colors = ["red", "green", "blue", "yellow", "purple"];

// Remove last element
array_pop($colors);

// Remove first element
array_shift($colors);

// Remove specific element
unset($colors[1]); // Removes "blue"

// Output
echo '<pre>';
print_r($colors);
echo '</pre>';

Output:

Array
(
    [0] => green
)

Array Iteration

Using foreach Loop

The foreach loop is the most common way to iterate through arrays:

php

$fruits = ["Apple", "Banana", "Orange", "Mango"];

// Basic foreach
foreach ($fruits as $fruit) {
    echo $fruit . "<br>";
}

// With key and value
$person = [
    "name" => "John",
    "age" => 30,
    "job" => "Developer"
];

foreach ($person as $key => $value) {
    echo "$key: $value<br>";
}

Output:

Apple
Banana
Orange
Mango
name: John
age: 30
job: Developer

Using for Loop (with Indexed Arrays)

php

$numbers = [10, 20, 30, 40, 50];

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

Output:

Index 0: 10
Index 1: 20
Index 2: 30
Index 3: 40
Index 4: 50

Using while and each (Legacy)

php

$colors = ["red", "green", "blue"];
reset($colors);

while (list($key, $value) = each($colors)) {
    echo "$key: $value<br>";
}

Note: The each() function is deprecated as of PHP 7.2. It's recommended to use foreach instead.

Common Array Functions

PHP provides many built-in functions for array manipulation:

Array Size and Properties

php

$fruits = ["Apple", "Banana", "Orange", "Mango", "Lemon"];

// Count elements
echo "Count: " . count($fruits) . "<br>";

// Check if element exists
echo "Contains Orange? " . (in_array("Orange", $fruits) ? "Yes" : "No") . "<br>";

// Get keys of array
$keys = array_keys($fruits);
echo "Keys: " . implode(", ", $keys) . "<br>";

// Check if key exists
echo "Has key 3? " . (array_key_exists(3, $fruits) ? "Yes" : "No") . "<br>";

Output:

Count: 5
Contains Orange? Yes
Keys: 0, 1, 2, 3, 4
Has key 3? Yes

Transformation Functions

php

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

// Map values
$squared = array_map(function($n) {
    return $n * $n;
}, $numbers);

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

// Reduce to single value
$sum = array_reduce($numbers, function($carry, $n) {
    return $carry + $n;
}, 0);

echo "Original: " . implode(", ", $numbers) . "<br>";
echo "Squared: " . implode(", ", $squared) . "<br>";
echo "Even numbers: " . implode(", ", $evenNumbers) . "<br>";
echo "Sum: $sum<br>";

Output:

Original: 1, 2, 3, 4, 5
Squared: 1, 4, 9, 16, 25
Even numbers: 2, 4
Sum: 15

Array Sorting

php

$fruits = ["banana", "apple", "orange", "grape"];
$numbers = [3, 1, 4, 1, 5, 9];
$assoc = ["d" => 4, "a" => 1, "c" => 3, "b" => 2];

// Sort indexed arrays
sort($fruits);  // Alphabetical
sort($numbers); // Numerical

// Sort associative arrays
asort($assoc);  // Sort by value, keep keys
ksort($assoc);  // Sort by key

// Reverse sort
rsort($fruits); // Reverse alphabetical

echo '<pre>';
echo "Sorted fruits: ";
print_r($fruits);
echo "Sorted numbers: ";
print_r($numbers);
echo "Sorted by value: ";
print_r($assoc); // After ksort
echo '</pre>';

Output:

Sorted fruits: 
Array
(
    [0] => orange
    [1] => grape
    [2] => banana
    [3] => apple
)
Sorted numbers: 
Array
(
    [0] => 1
    [1] => 1
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 9
)
Sorted by value: 
Array
(
    [a] => 1
    [b] => 2
    [c] => 3
    [d] => 4
)

Array Combining and Merging

php

$firstNames = ["John", "Jane"];
$lastNames = ["Doe", "Smith"];

// Combine (keys from first, values from second)
$fullNames = array_combine($firstNames, $lastNames);

// Merge arrays
$array1 = ["a" => "apple", "b" => "banana"];
$array2 = ["b" => "berry", "c" => "cherry"];
$merged = array_merge($array1, $array2);

echo '<pre>';
echo "Combined arrays: ";
print_r($fullNames);
echo "Merged arrays: ";
print_r($merged);
echo '</pre>';

Output:

Combined arrays: 
Array
(
    [John] => Doe
    [Jane] => Smith
)
Merged arrays: 
Array
(
    [a] => apple
    [b] => berry
    [c] => cherry
)

Array Operators

PHP provides specific operators for array operations:

php

$a = ["a" => "apple", "b" => "banana"];
$b = ["b" => "berry", "c" => "cherry"];

// Union
$union = $a + $b;

// Equality comparison
$c = ["a" => "apple", "b" => "banana"];
$equal = ($a == $c); // true
$identical = ($a === $c); // true

echo '<pre>';
echo "Union result: ";
print_r($union);
echo "Equal: " . ($equal ? "true" : "false") . "<br>";
echo "Identical: " . ($identical ? "true" : "false") . "<br>";
echo '</pre>';

Output:

Union result: 
Array
(
    [a] => apple
    [b] => banana
    [c] => cherry
)
Equal: true
Identical: true

Advanced Array Operations

Array Slicing

php

$fruits = ["Apple", "Banana", "Orange", "Mango", "Grapes"];

// Extract a portion
$slice = array_slice($fruits, 1, 2);  // Start at index 1, take 2 elements

// Remove and replace elements
$removed = array_splice($fruits, 2, 1, ["Peach", "Pineapple"]);

echo '<pre>';
echo "Sliced array: ";
print_r($slice);
echo "After splice: ";
print_r($fruits);
echo "Removed items: ";
print_r($removed);
echo '</pre>';

Output:

Sliced array: 
Array
(
    [0] => Banana
    [1] => Orange
)
After splice: 
Array
(
    [0] => Apple
    [1] => Banana
    [2] => Peach
    [3] => Pineapple
    [4] => Mango
    [5] => Grapes
)
Removed items: 
Array
(
    [0] => Orange
)

Array Diff and Intersect

php

$array1 = ["apple", "banana", "cherry", "date"];
$array2 = ["banana", "cherry", "elderberry", "fig"];

// Find differences
$diff = array_diff($array1, $array2);  // In array1 but not in array2

// Find common elements
$intersect = array_intersect($array1, $array2);  // In both arrays

echo '<pre>';
echo "Difference: ";
print_r($diff);
echo "Intersection: ";
print_r($intersect);
echo '</pre>';

Output:

Difference: 
Array
(
    [0] => apple
    [3] => date
)
Intersection: 
Array
(
    [1] => banana
    [2] => cherry
)

Array Visualization

Let's visualize how different array operations transform arrays:

Practical Examples

Example 1: User Management System

php

// User database simulation
$users = [
    [
        "id" => 1,
        "name" => "John Doe",
        "email" => "[email protected]",
        "role" => "admin",
        "active" => true
    ],
    [
        "id" => 2,
        "name" => "Jane Smith",
        "email" => "[email protected]",
        "role" => "editor",
        "active" => true
    ],
    [
        "id" => 3,
        "name" => "Bob Johnson",
        "email" => "[email protected]",
        "role" => "user",
        "active" => false
    ]
];

// Function to find a user by ID
function findUserById($users, $id) {
    foreach ($users as $user) {
        if ($user["id"] === $id) {
            return $user;
        }
    }
    return null;
}

// Filter active users
$activeUsers = array_filter($users, function($user) {
    return $user["active"] === true;
});

// Get all user emails (for newsletter)
$emails = array_map(function($user) {
    return $user["email"];
}, $users);

// Group users by role
$usersByRole = [];
foreach ($users as $user) {
    $role = $user["role"];
    if (!isset($usersByRole[$role])) {
        $usersByRole[$role] = [];
    }
    $usersByRole[$role][] = $user;
}

// Example usage
$user = findUserById($users, 2);
echo "User found: " . $user["name"] . "<br>";

echo "Active users: " . count($activeUsers) . "<br>";

echo "User emails: " . implode(", ", $emails) . "<br>";

echo '<pre>';
echo "Users by role: ";
print_r($usersByRole);
echo '</pre>';

Output:

User found: Jane Smith
Active users: 2
User emails: [email protected], [email protected], [email protected]
Users by role: 
Array
(
    [admin] => Array
        (
            [0] => Array
                (
                    [id] => 1
                    [name] => John Doe
                    [email] => [email protected]
                    [role] => admin
                    [active] => 1
                )
        )
    [editor] => Array
        (
            [0] => Array
                (
                    [id] => 2
                    [name] => Jane Smith
                    [email] => [email protected]
                    [role] => editor
                    [active] => 1
                )
        )
    [user] => Array
        (
            [0] => Array
                (
                    [id] => 3
                    [name] => Bob Johnson
                    [email] => [email protected]
                    [role] => user
                    [active] => 
                )
        )
)

Example 2: Shopping Cart

php

// Product catalog
$products = [
    1 => ["name" => "Laptop", "price" => 999.99],
    2 => ["name" => "Smartphone", "price" => 499.50],
    3 => ["name" => "Headphones", "price" => 149.75],
    4 => ["name" => "Tablet", "price" => 299.99]
];

// Shopping cart
$cart = [
    ["product_id" => 1, "quantity" => 1],
    ["product_id" => 3, "quantity" => 2],
    ["product_id" => 4, "quantity" => 1]
];

// Calculate cart total
function calculateTotal($cart, $products) {
    $total = 0;
    foreach ($cart as $item) {
        $productId = $item["product_id"];
        $quantity = $item["quantity"];
        
        if (isset($products[$productId])) {
            $price = $products[$productId]["price"];
            $total += $price * $quantity;
        }
    }
    return $total;
}

// Function to display cart with product details
function displayCart($cart, $products) {
    $cartDetails = [];
    
    foreach ($cart as $item) {
        $productId = $item["product_id"];
        $quantity = $item["quantity"];
        
        if (isset($products[$productId])) {
            $product = $products[$productId];
            $cartDetails[] = [
                "name" => $product["name"],
                "price" => $product["price"],
                "quantity" => $quantity,
                "subtotal" => $product["price"] * $quantity
            ];
        }
    }
    
    return $cartDetails;
}

// Example usage
$cartTotal = calculateTotal($cart, $products);
$cartDetails = displayCart($cart, $products);

echo "Cart Total: $" . number_format($cartTotal, 2) . "<br>";

echo '<pre>';
echo "Cart Contents: ";
print_r($cartDetails);
echo '</pre>';

Output:

Cart Total: $1,599.49
Cart Contents: 
Array
(
    [0] => Array
        (
            [name] => Laptop
            [price] => 999.99
            [quantity] => 1
            [subtotal] => 999.99
        )
    [1] => Array
        (
            [name] => Headphones
            [price] => 149.75
            [quantity] => 2
            [subtotal] => 299.5
        )
    [2] => Array
        (
            [name] => Tablet
            [price] => 299.99
            [quantity] => 1
            [subtotal] => 299.99
        )
)

Summary

Array operations are foundational to PHP programming. In this guide, we've covered:

1. Creating Arrays: Indexed, associative, and multidimensional arrays
2. Accessing and Modifying: Adding, changing, and removing elements
3. Iteration: Different approaches to loop through arrays
4. Array Functions: Essential built-in functions for manipulation
5. Array Operators: Union and comparison operations
6. Advanced Operations: Working with slices, differences, and intersections
7. Practical Examples: Real-world applications of array operations

Mastering these array operations will significantly improve your PHP programming skills and enable you to build more complex and efficient applications.

Additional Resources

• PHP Manual: Arrays
• PHP Manual: Array Functions

Exercises

1. Create a function that takes an array of numbers and returns a new array containing only the even numbers.
2. Write a script that takes two arrays and returns their union, intersection, and difference.
3. Create a multidimensional array representing a simple database of products with categories. Then write functions to:
   • Find all products in a specific category
   • Calculate the total value of all products
   • Find the most expensive product
4. Build a simple to-do list application that uses arrays to store tasks. Include functionality to add, remove, and mark tasks as complete.
5. Challenge: Create a function that flattens a multidimensional array into a single-dimensional array while preserving the keys.