Arrays in PHP - Part 1 — Basics and Data Structure

Arrays are one of the most important data structures in PHP. Arrays allow you to store and organize multiple values in a single variable. In this article we’ll cover the basics of working with arrays, their types, and the most common use cases.

In PHP an array lets you store many values at once, which makes it easier to manage data effectively. Arrays help group information logically and operate on it conveniently in your code. This is especially useful when building web applications or information systems.

What are arrays in PHP?

An array in PHP is an ordered map that links values with keys. It is an extremely flexible data structure that can act as a traditional array, a list, an associative array (hash table), a dictionary, a collection, a stack, a queue, and many other structures.

<?php // Basic array $fruits = array(“apple”, “banana”, “orange”);

// Short syntax (since PHP 5.4) $colors = [“red”, “blue”, “green”]; ?>

Indexed arrays vs associative arrays

Indexed arrays

Indexed arrays use numeric indexes that start at 0 by default:

<?php // Creating an indexed array $numbers = [10, 20, 30, 40, 50];

// Accessing elements echo $numbers[0]; // Outputs: 10 echo $numbers[2]; // Outputs: 30

// Adding elements $numbers[] = 60; // Appends $numbers[10] = 100; // Sets index 10

// Checking length echo count($numbers); // Outputs number of elements ?>

Associative arrays

Associative arrays use named keys instead of numeric indexes. PHP arrays (associative arrays) let you store multiple values under descriptive keys. In PHP, array indices can be not only numbers but also strings. This makes arrays very flexible and easy to adapt to different programming needs. Arrays in PHP can also hold different data types like numbers, strings, or even other arrays — enabling complex data structures and efficient management within applications.

<?php // Creating an associative array $person = [ “name” => “Jan”, “surname” => “Kowalski”, “age” => 30, “city” => “Warsaw” ];

// Accessing elements echo $person[“name”]; // Outputs: Jan echo $person[“age”]; // Outputs: 30

// Adding new elements $person[“email”] = “jan@example.com”; $person[“phone”] = “123-456-789”;

// Modifying existing elements $person[“age”] = 31; ?>

Identifying array elements

PHP offers several ways to check array contents, including array_key_exists(), isset(), and empty(). These functions let developers manage array data effectively and verify the presence of keys or values depending on the needs. They are essential for safe and robust data handling in PHP:

<?php $data = [ “user” => “admin”, “password” => “secret”, “role” => “administrator” ];

// Check if a key exists if (array_key_exists(“user”, $data)) { echo “Key ‘user’ exists”; }

// Check if a value exists if (in_array(“admin”, $data)) { echo “Value ‘admin’ exists in the array”; }

// Check if value is set if (isset($data[“password”])) { echo “Password is set”; }

// Check if not empty if (!empty($data[“role”])) { echo “User role: “ . $data[“role”]; } ?>

Storing different data types

PHP arrays can store values of various types. An array can contain numbers, strings, or even other arrays. This capability makes PHP arrays a very flexible tool for storing and manipulating data in applications.

<?php $mixed_data = [ “string” => “This is text”, “number” => 42, “float” => 3.14, “boolean” => true, “null_value” => null, “array” => [1, 2, 3], “object” => new stdClass() ];

// Iterate through the array foreach ($mixed_data as $key => $value) { echo $key . “: “ . gettype($value) . “\n”; } ?>

Multidimensional arrays

Arrays can contain other arrays, creating multidimensional structures. With multidimensional arrays in PHP, you can build nested data where each element may be another array. For example, you can have an array of users where each user has its own data like name, surname, and age. Multidimensional arrays make it easy to manage more complex data structures useful in advanced PHP projects:

<?php // Two-dimensional array $matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ];

// Accessing elements echo $matrix[1][2]; // Outputs: 6

// Multidimensional associative array $users = [ [ “id” => 1, “name” => “Jan Kowalski”, “email” => “jan@example.com”, “skills” => [“PHP”, “JavaScript”, “MySQL”] ], [ “id” => 2, “name” => “Anna Nowak”, “email” => “anna@example.com”, “skills” => [“Python”, “Django”, “PostgreSQL”] ] ];

// Access nested elements echo $users[0][“name”]; // Jan Kowalski echo $users[1][“skills”][0]; // Python ?>

Basic array operations

How to add elements to an array?

The array_push function adds elements at the end, while array_unshift adds them at the beginning. You can also insert elements at a specific position with array_splice.

<?php $fruits = [“apple”, “banana”];

// Add at the end $fruits[] = “orange”; array_push($fruits, “pear”, “plum”);

// Add at the beginning array_unshift($fruits, “strawberry”);

// Insert at specific position array_splice($fruits, 2, 0, [“kiwi”, “mango”]);

print_r($fruits); ?>

Removing elements is analogous to adding — use array_pop for the last element and array_shift for the first.

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

// Remove last element $last = array_pop($numbers);

// Remove first element $first = array_shift($numbers);

// Remove a specific element unset($numbers[1]);

// Remove multiple elements array_splice($numbers, 1, 2);

print_r($numbers); ?>

Practical usage examples

Simple examples include storing configuration, form data, and navigation menus.

1. Storing configuration

<?php $config = [ “database” => [ “host” => “localhost”, “port” => 3306, “name” => “myapp”, “charset” => “utf8” ], “cache” => [ “enabled” => true, “ttl” => 3600 ], “debug” => false ];

// Access config $db_host = $config[“database”][“host”]; ?>

2. Storing form data

<?php if ($_POST) { $form_data = [ “name” => $_POST[“name”] ?? “”, “email” => $_POST[“email”] ?? “”, “message” => $_POST[“message”] ?? “”, “timestamp” => date(“Y-m-d H:i:s”) ];

// Validate
$errors = [];

if (empty($form_data["name"])) {
    $errors[] = "Name is required";
}

if (!filter_var($form_data["email"], FILTER_VALIDATE_EMAIL)) {
    $errors[] = "Invalid email address";
}

if (empty($errors)) {
    // Process data
    processFormData($form_data);
} } ?>

3. Building a navigation menu

<?php $navigation = [ [ “title” => “Home”, “url” => “/”, “active” => true ], [ “title” => “About”, “url” => “/about”, “active” => false ], [ “title” => “Services”, “url” => “/services”, “active” => false, “submenu” => [ [“title” => “Web Development”, “url” => “/services/web-design”], [“title” => “SEO”, “url” => “/services/seo”], [“title” => “Marketing”, “url” => “/services/marketing”] ] ], [ “title” => “Contact”, “url” => “/contact”, “active” => false ] ];

// Generate HTML menu function generateMenu($items) { echo “<ul>”; foreach ($items as $item) { $class = $item[“active”] ? “active” : “”; echo “<li class='{$class}'>”; echo “{$item[“title”]}”;

    if (isset($item["submenu"])) {
        generateMenu($item["submenu"]);
    }
    
    echo "</li>";
}
echo "</ul>"; } ?>

Common mistakes and how to avoid them

1. Checking for key existence

<?php // WRONG - may generate a Notice echo $array[“key”];

// CORRECT echo $array[“key”] ?? “default value”;

// or if (isset($array[“key”])) { echo $array[“key”]; } ?>

2. Iterating through arrays

<?php $data = [“a” => 1, “b” => 2, “c” => 3];

// CORRECT - with keys foreach ($data as $key => $value) { echo “{$key}: {$value}\n”; }

// CORRECT - values only foreach ($data as $value) { echo $value . “\n”; } ?>

QA — Arrays

Q: Can I store different data types in a PHP array? A: Yes, PHP arrays can hold multiple data types simultaneously, such as numbers, strings, booleans, other arrays, or objects — allowing you to create complex data structures easily.

Q: What happens if I access a non-existent key in an array? A: PHP will emit a Notice: Undefined index, so it’s good practice to check with isset() or use the null coalescing operator ??.

Q: How do I add a new element to an associative array? A: Assign a value to a new key, e.g. $person["email"] = "test@example.com";.

Summary

Arrays in PHP are a powerful tool for effective data management. In this first part we covered:

• Differences between indexed and associative arrays

• Methods to identify elements

• Basic operations for adding and removing elements

• Practical example usages

In the second part of this article Post #62 Arrays Part II we’ll explore advanced techniques for working with arrays, including manipulation functions, sorting, filtering, and conversions between different data formats.

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