PHP Array Functions I

PHP provides dozens of built-in array functions. In this lesson, we'll cover the essential functions for counting, searching, and extracting information from arrays.

Counting Elements

<?php
$fruits = ["Apple", "Banana", "Cherry"];
echo count($fruits);  // 3

$nested = ["a", ["b", "c"], "d"];
echo count($nested);                    // 3 (top level only)
echo count($nested, COUNT_RECURSIVE);   // 5 (all elements)

// Empty array check
$empty = [];
if (count($empty) === 0) {
    echo "Array is empty";
}
?>

Click Run to execute your code

Checking for Values

in_array()

Check if a value exists in an array:

<?php
$fruits = ["Apple", "Banana", "Cherry"];

// Basic usage
in_array("Banana", $fruits);  // true
in_array("Grape", $fruits);   // false

// Case-sensitive!
in_array("apple", $fruits);   // false
in_array("Apple", $fruits);   // true

// Strict mode (checks type too)
$mixed = [1, 2, "3", 4];
in_array(3, $mixed);          // true (loose comparison)
in_array(3, $mixed, true);    // false (strict comparison)
in_array("3", $mixed, true);  // true
?>

Finding Keys

array_search()

Find the key of a value:

<?php
$fruits = ["apple", "banana", "cherry"];

// Find key
$key = array_search("banana", $fruits);
echo $key;  // 1

// Not found returns false
$key = array_search("grape", $fruits);
if ($key === false) {
    echo "Not found";
}

// With duplicates, returns first match
$items = ["a", "b", "c", "b"];
echo array_search("b", $items);  // 1 (first occurrence)
?>

Checking for Keys

array_key_exists() vs isset()

<?php
$data = [
    "name" => "John",
    "email" => null,
    "active" => false
];

// array_key_exists - checks only if key exists
array_key_exists("name", $data);   // true
array_key_exists("email", $data);  // true (even though null)
array_key_exists("phone", $data);  // false

// isset - checks if key exists AND is not null
isset($data["name"]);   // true
isset($data["email"]);  // false (null value)
isset($data["phone"]);  // false
?>

Extracting Keys and Values

array_keys()

<?php
$person = ["name" => "John", "age" => 30, "city" => "NYC"];

// Get all keys
$keys = array_keys($person);
print_r($keys);  // ["name", "age", "city"]

// Get keys for specific value
$scores = ["Alice" => 95, "Bob" => 88, "Carol" => 95];
$topScorers = array_keys($scores, 95);
print_r($topScorers);  // ["Alice", "Carol"]
?>

array_values()

<?php
$person = ["name" => "John", "age" => 30, "city" => "NYC"];

// Get all values (reindexed)
$values = array_values($person);
print_r($values);  // ["John", 30, "NYC"]

// Useful for reindexing after unset
$arr = [0 => "a", 1 => "b", 2 => "c"];
unset($arr[1]);
print_r($arr);  // [0 => "a", 2 => "c"] - gap in indices

$arr = array_values($arr);
print_r($arr);  // [0 => "a", 1 => "c"] - reindexed
?>

First and Last Elements

<?php
$queue = ["first", "second", "third", "last"];

// Get first element
$first = reset($queue);  // "first" (moves pointer to start)

// Get last element
$last = end($queue);     // "last" (moves pointer to end)

// Get current element
$current = current($queue);  // "last" (pointer is at end)

// PHP 7.3+: Get first/last key without moving pointer
$firstKey = array_key_first($queue);  // 0
$lastKey = array_key_last($queue);    // 3
?>

Practical Examples

<?php
// Check if user role is allowed
$allowedRoles = ["admin", "editor", "moderator"];
$userRole = "editor";

if (in_array($userRole, $allowedRoles, true)) {
    echo "Access granted";
}

// Find user by email
$users = [
    ["id" => 1, "email" => "[email protected]"],
    ["id" => 2, "email" => "[email protected]"],
    ["id" => 3, "email" => "[email protected]"]
];

$searchEmail = "[email protected]";
$foundUser = null;

foreach ($users as $user) {
    if ($user["email"] === $searchEmail) {
        $foundUser = $user;
        break;
    }
}

// Get unique values
$tags = ["php", "javascript", "php", "python", "javascript"];
$uniqueTags = array_unique($tags);
print_r($uniqueTags);  // ["php", "javascript", "python"]
?>

Quick Reference

Exercise: Search System

<?php
$products = [
    ["id" => 1, "name" => "Laptop", "category" => "Electronics", "price" => 999],
    ["id" => 2, "name" => "Mouse", "category" => "Electronics", "price" => 29],
    ["id" => 3, "name" => "Desk", "category" => "Furniture", "price" => 199],
    ["id" => 4, "name" => "Chair", "category" => "Furniture", "price" => 149],
    ["id" => 5, "name" => "Notebook", "category" => "Stationery", "price" => 5]
];

// Find product by ID
function findProductById($products, $id) {
    foreach ($products as $product) {
        if ($product["id"] === $id) {
            return $product;
        }
    }
    return null;
}

// Check if category exists
function categoryExists($products, $category) {
    foreach ($products as $product) {
        if ($product["category"] === $category) {
            return true;
        }
    }
    return false;
}

// Get unique categories
function getCategories($products) {
    $categories = [];
    foreach ($products as $product) {
        if (!in_array($product["category"], $categories)) {
            $categories[] = $product["category"];
        }
    }
    return $categories;
}

// Count products per category
function countByCategory($products) {
    $counts = [];
    foreach ($products as $product) {
        $cat = $product["category"];
        if (!isset($counts[$cat])) {
            $counts[$cat] = 0;
        }
        $counts[$cat]++;
    }
    return $counts;
}

// Test the functions
echo "Product #2: ";
print_r(findProductById($products, 2));

echo "Electronics exists: " . (categoryExists($products, "Electronics") ? "Yes" : "No") . "\n";

echo "Categories: " . implode(", ", getCategories($products)) . "\n";

echo "Products per category:\n";
print_r(countByCategory($products));
?>

Summary

What's Next?

Now let's explore Array Functions II - functions for modifying arrays: adding, removing, merging, and slicing elements!