PHP Arrays

What are Arrays?

Arrays store multiple values in a single variable. PHP supports three types: indexed (numeric keys), associative (named keys), and multidimensional (arrays within arrays).

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Indexed Arrays

The simplest array type. An ordered list where each value has a numeric index starting at 0.

// Short syntax (recommended)
$fruits = ["apple", "banana", "orange"];

// Or using array()
$fruits = array("apple", "banana", "orange");

Access elements by their index:

$colors = ["Red", "Green", "Blue"];

echo $colors[0];  // Red
echo $colors[2];  // Blue

// Modify an element
$colors[1] = "Yellow";

// Add to the end
$colors[] = "Purple";

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Associative Arrays

Associative arrays use string keys instead of numeric indices. PHP’s superglobals like $_POST and $_GET work this way.

$person = [
    "name" => "John Doe",
    "age" => 30,
    "city" => "New York"
];

Access elements by their key:

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

echo $user["email"];  // john@example.com

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

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

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Multidimensional Arrays

Arrays can contain other arrays, which is useful for representing structured data like database rows or nested configurations.

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

// Nested associative array
$products = [
    "laptop" => [
        "brand" => "Dell",
        "price" => 800,
        "specs" => ["RAM" => "8GB", "Storage" => "256GB"]
    ],
    "phone" => [
        "brand" => "iPhone",
        "price" => 999
    ]
];

Access nested elements by chaining brackets:

echo $students[0][0];              // John
echo $products["laptop"]["brand"]; // Dell
echo $products["laptop"]["specs"]["RAM"]; // 8GB

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Modifying Arrays

Adding Elements

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

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

Removing Elements

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

array_pop($fruits);    // Remove last element
array_shift($fruits);  // Remove first element
unset($fruits[1]);     // Remove by index

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

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Looping Through Arrays

The foreach loop is the most common way to iterate over arrays.

// Indexed array - just values
$colors = ["Red", "Green", "Blue"];
foreach ($colors as $color) {
    echo $color . "\n";
}

// Associative array - keys and values
$user = ["name" => "John", "email" => "john@example.com"];
foreach ($user as $key => $value) {
    echo "$key: $value\n";
}

For indexed arrays where you need the index, a for loop works well:

$numbers = [10, 20, 30];
for ($i = 0; $i < count($numbers); $i++) {
    echo "Index $i: " . $numbers[$i] . "\n";
}

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Common Array Functions

Getting Information

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

count($fruits);                      // 3
empty($fruits);                      // false
in_array("apple", $fruits);          // true
array_key_exists("name", $person);   // true/false
array_search("banana", $fruits);     // 1 (the index)

Transforming Arrays

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

sort($numbers);                // Sort ascending
rsort($numbers);               // Sort descending
array_reverse($numbers);       // Reverse order
array_unique($numbers);        // Remove duplicates

// Filter elements
$evens = array_filter($numbers, fn($n) => $n % 2 == 0);

// Transform each element
$doubled = array_map(fn($n) => $n * 2, $numbers);

Combining Arrays

$a = ["a", "b"];
$b = ["c", "d"];

array_merge($a, $b);       // ["a", "b", "c", "d"]
array_chunk($a, 2);        // Split into chunks of 2
array_slice($a, 1, 2);     // Extract portion

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Practical Example: Shopping Cart

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

$total = 0;
foreach ($cart as $item => $details) {
    $subtotal = $details["price"] * $details["qty"];
    $total += $subtotal;
    echo "$item: \$$subtotal\n";
}
echo "Total: \$$total";

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Tips

Before accessing an array element, check that the key exists to avoid errors:

if (isset($person["email"])) {
    echo $person["email"];
}

Use type hints in functions that expect arrays:

function calculateTotal(array $prices): float {
    return array_sum($prices);
}