Array Functions

PHP provides an extensive collection of built-in functions for array manipulation. This comprehensive guide covers the most important array functions organized by their primary use cases. PHP Array Functions - Full Documentation ↗

Array Information & Validation

These functions help you inspect and validate arrays.

count() - Get Array Length

Returns the number of elements in an array.

$fruits = ['apple', 'banana', 'orange'];
echo count($fruits);  // Outputs: 3

// Multidimensional arrays
$users = [
    ['name' => 'John', 'age' => 25],
    ['name' => 'Jane', 'age' => 30]
];
echo count($users);           // Outputs: 2 (top level)
echo count($users, COUNT_RECURSIVE);  // Outputs: 6 (all elements)

is_array() - Check if Variable is Array

Determines whether a variable is an array.

$data = ['apple', 'banana'];
$string = 'hello';

var_dump(is_array($data));    // bool(true)
var_dump(is_array($string));  // bool(false)

array_key_exists() - Check if Key Exists

Checks if a specified key exists in an array.

$user = ['name' => 'John', 'email' => 'john@example.com'];

if (array_key_exists('name', $user)) {
    echo "Name exists: " . $user['name'];
}

// Note: Different from isset() - works with null values
$data = ['key' => null];
var_dump(array_key_exists('key', $data));  // bool(true)
var_dump(isset($data['key']));             // bool(false)

empty() and isset() - Check Values

$data = ['name' => 'John', 'age' => 0, 'email' => ''];

var_dump(isset($data['name']));    // bool(true)
var_dump(empty($data['age']));     // bool(true) - 0 is empty
var_dump(empty($data['email']));   // bool(true) - empty string
var_dump(isset($data['phone']));   // bool(false) - doesn't exist

---

Array Manipulation & Modification

Functions for adding, removing, and modifying array elements.

Adding Elements

array_push() - Add to End

Adds one or more elements to the end of an array.

$colors = ['red', 'green'];
array_push($colors, 'blue', 'yellow');
print_r($colors);  // ['red', 'green', 'blue', 'yellow']

// Alternative syntax (PHP 7.4+)
$colors[] = 'purple';  // Same as array_push($colors, 'purple')

array_unshift() - Add to Beginning

Adds elements to the beginning of an array.

$numbers = [2, 3, 4];
array_unshift($numbers, 0, 1);
print_r($numbers);  // [0, 1, 2, 3, 4]

array_splice() - Insert at Specific Position

Removes and replaces elements at any position.

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

// Insert 'grape' at position 1 without removing anything
array_splice($fruits, 1, 0, ['grape']);
print_r($fruits);  // ['apple', 'grape', 'banana', 'orange']

// Replace 'banana' with 'mango'
array_splice($fruits, 2, 1, ['mango']);
print_r($fruits);  // ['apple', 'grape', 'mango', 'orange']

Removing Elements

array_pop() - Remove from End

Removes and returns the last element.

$stack = ['item1', 'item2', 'item3'];
$lastItem = array_pop($stack);
echo $lastItem;  // 'item3'
print_r($stack); // ['item1', 'item2']

array_shift() - Remove from Beginning

Removes and returns the first element.

$queue = ['first', 'second', 'third'];
$firstItem = array_shift($queue);
echo $firstItem;  // 'first'
print_r($queue);  // ['second', 'third']

unset() - Remove Specific Elements

Removes elements by key.

$data = ['a' => 1, 'b' => 2, 'c' => 3];
unset($data['b']);
print_r($data);  // ['a' => 1, 'c' => 3]

// Remove multiple elements
unset($data['a'], $data['c']);
print_r($data);  // []

Array Keys and Values

array_keys() - Get All Keys

Returns an array of all keys.

$person = ['name' => 'John', 'age' => 30, 'city' => 'NYC'];
$keys = array_keys($person);
print_r($keys);  // ['name', 'age', 'city']

// Get keys for specific value
$colors = ['red', 'blue', 'red', 'green'];
$redKeys = array_keys($colors, 'red');
print_r($redKeys);  // [0, 2]

array_values() - Get All Values

Returns an array of all values with numeric keys.

$person = ['name' => 'John', 'age' => 30, 'city' => 'NYC'];
$values = array_values($person);
print_r($values);  // ['John', 30, 'NYC']

array_flip() - Swap Keys and Values

Exchanges keys with their associated values.

$original = ['a' => 1, 'b' => 2, 'c' => 3];
$flipped = array_flip($original);
print_r($flipped);  // [1 => 'a', 2 => 'b', 3 => 'c']

---

Array Search & Filtering

Functions for finding and filtering array elements.

in_array() - Check if Value Exists

Searches for a value in an array.

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

var_dump(in_array('banana', $fruits));  // bool(true)
var_dump(in_array('grape', $fruits));   // bool(false)

// Strict type checking
$numbers = [1, 2, 3, '4'];
var_dump(in_array(4, $numbers));        // bool(true) - loose comparison
var_dump(in_array(4, $numbers, true));  // bool(false) - strict comparison

array_search() - Find Key by Value

Returns the key of the first matching value.

$fruits = ['apple', 'banana', 'orange'];
$key = array_search('banana', $fruits);
echo $key;  // Outputs: 1

// Returns false if not found
$key = array_search('grape', $fruits);
var_dump($key);  // bool(false)

// With strict comparison
$numbers = [1, 2, 3, '4'];
$key = array_search(4, $numbers, true);
var_dump($key);  // bool(false) - strict comparison

array_filter() - Filter Array Elements

Filters elements using a callback function.

$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// Filter even numbers
$evenNumbers = array_filter($numbers, function($n) {
    return $n % 2 === 0;
});
print_r($evenNumbers);  // [2, 4, 6, 8, 10]

// Filter by key and value
$users = [
    'john' => ['age' => 25, 'active' => true],
    'jane' => ['age' => 17, 'active' => true],
    'bob' => ['age' => 30, 'active' => false]
];

$activeAdults = array_filter($users, function($user, $key) {
    return $user['age'] >= 18 && $user['active'];
}, ARRAY_FILTER_USE_BOTH);

print_r($activeAdults);  // Only 'john'

array_column() - Extract Column from 2D Array

Extracts a single column from a multidimensional array.

$users = [
    ['id' => 1, 'name' => 'John', 'email' => 'john@example.com'],
    ['id' => 2, 'name' => 'Jane', 'email' => 'jane@example.com'],
    ['id' => 3, 'name' => 'Bob', 'email' => 'bob@example.com']
];

// Extract names
$names = array_column($users, 'name');
print_r($names);  // ['John', 'Jane', 'Bob']

// Extract emails with ID as key
$emails = array_column($users, 'email', 'id');
print_r($emails);  // [1 => 'john@example.com', 2 => 'jane@example.com', ...]

array_unique() - Remove Duplicate Values

Removes duplicate values from an array.

$colors = ['red', 'blue', 'red', 'green', 'blue'];
$uniqueColors = array_unique($colors);
print_r($uniqueColors);  // ['red', 'blue', 'green']

// With associative arrays
$data = [
    'a' => 'apple',
    'b' => 'banana',
    'c' => 'apple',
    'd' => 'orange'
];
$unique = array_unique($data);
print_r($unique);  // ['a' => 'apple', 'b' => 'banana', 'd' => 'orange']

array_intersect() - Find Common Values

Returns values that exist in all arrays.

$array1 = ['a', 'b', 'c', 'd'];
$array2 = ['b', 'c', 'd', 'e'];
$array3 = ['c', 'd', 'e', 'f'];

$common = array_intersect($array1, $array2, $array3);
print_r($common);  // ['c', 'd']

array_diff() - Find Different Values

Returns values from the first array that are not in other arrays.

$array1 = ['a', 'b', 'c', 'd'];
$array2 = ['b', 'c'];

$diff = array_diff($array1, $array2);
print_r($diff);  // ['a', 'd']

---

Array Transformation

Functions that transform arrays into different structures or apply operations to all elements.

array_map() - Apply Function to Elements

Applies a callback function to each element.

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

// Square each number
$squared = array_map(function($n) {
    return $n * $n;
}, $numbers);
print_r($squared);  // [1, 4, 9, 16, 25]

// Work with multiple arrays
$names = ['John', 'Jane', 'Bob'];
$ages = [25, 30, 35];

$combined = array_map(function($name, $age) {
    return "$name is $age years old";
}, $names, $ages);
print_r($combined);  // ['John is 25 years old', 'Jane is 30 years old', ...]

array_walk() - Apply Function with Side Effects

Applies a function to each element, allowing modification of the original array.

$prices = ['apple' => 1.50, 'banana' => 0.75, 'orange' => 2.00];

// Add tax to each price
array_walk($prices, function(&$price, $item) {
    $price = round($price * 1.08, 2);  // 8% tax
});
print_r($prices);  // ['apple' => 1.62, 'banana' => 0.81, 'orange' => 2.16]

// With additional data
array_walk($prices, function(&$price, $item, $taxRate) {
    $price = round($price * (1 + $taxRate), 2);
}, 0.05);  // 5% additional tax

array_reduce() - Reduce Array to Single Value

Iteratively reduces an array to a single value using a callback.

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

// Sum all numbers
$sum = array_reduce($numbers, function($carry, $item) {
    return $carry + $item;
}, 0);
echo $sum;  // 15

// Find maximum value
$max = array_reduce($numbers, function($carry, $item) {
    return max($carry, $item);
}, PHP_INT_MIN);
echo $max;  // 5

// Build a string
$words = ['Hello', 'World', 'PHP'];
$sentence = array_reduce($words, function($carry, $word) {
    return $carry . ' ' . $word;
}, '');
echo trim($sentence);  // "Hello World PHP"

array_chunk() - Split Array into Chunks

Splits an array into chunks of specified size.

$data = [1, 2, 3, 4, 5, 6, 7, 8, 9];

// Split into chunks of 3
$chunks = array_chunk($data, 3);
print_r($chunks);  // [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

// Preserve keys
$associativeData = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];
$chunks = array_chunk($associativeData, 2, true);
print_r($chunks);  // [['a' => 1, 'b' => 2], ['c' => 3, 'd' => 4]]

array_slice() - Extract Portion of Array

Returns a slice of an array.

$fruits = ['apple', 'banana', 'orange', 'grape', 'kiwi'];

// Get elements 1-3
$slice = array_slice($fruits, 1, 3);
print_r($slice);  // ['banana', 'orange', 'grape']

// Get last 2 elements
$lastTwo = array_slice($fruits, -2);
print_r($lastTwo);  // ['grape', 'kiwi']

// Preserve keys
$data = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];
$slice = array_slice($data, 1, 2, true);
print_r($slice);  // ['b' => 2, 'c' => 3]

array_reverse() - Reverse Array Order

Reverses the order of array elements.

$numbers = [1, 2, 3, 4, 5];
$reversed = array_reverse($numbers);
print_r($reversed);  // [5, 4, 3, 2, 1]

// Preserve keys
$data = ['first' => 1, 'second' => 2, 'third' => 3];
$reversed = array_reverse($data, true);
print_r($reversed);  // ['third' => 3, 'second' => 2, 'first' => 1]

implode() and explode() - String Conversion

Convert between arrays and strings.

// Array to string
$fruits = ['apple', 'banana', 'orange'];
$string = implode(', ', $fruits);
echo $string;  // "apple, banana, orange"

// String to array
$text = "one,two,three,four";
$array = explode(',', $text);
print_r($array);  // ['one', 'two', 'three', 'four']

// Limit splits
$limitedArray = explode(',', $text, 2);
print_r($limitedArray);  // ['one', 'two,three,four']

---

Array Comparison & Merging

Functions for combining and comparing arrays.

array_merge() - Merge Arrays

Merges one or more arrays together.

$array1 = ['a', 'b', 'c'];
$array2 = ['d', 'e', 'f'];
$merged = array_merge($array1, $array2);
print_r($merged);  // ['a', 'b', 'c', 'd', 'e', 'f']

// With associative arrays
$defaults = ['color' => 'blue', 'size' => 'medium'];
$userPrefs = ['color' => 'red', 'style' => 'modern'];
$config = array_merge($defaults, $userPrefs);
print_r($config);  // ['color' => 'red', 'size' => 'medium', 'style' => 'modern']

array_merge_recursive() - Recursive Merge

Merges arrays recursively, combining values with same keys into arrays.

$array1 = [
    'colors' => ['red', 'blue'],
    'sizes' => ['S', 'M']
];

$array2 = [
    'colors' => ['green', 'yellow'],
    'sizes' => ['L', 'XL'],
    'styles' => ['modern', 'classic']
];

$merged = array_merge_recursive($array1, $array2);
print_r($merged);
// Output:
// [
//     'colors' => ['red', 'blue', 'green', 'yellow'],
//     'sizes' => ['S', 'M', 'L', 'XL'],
//     'styles' => ['modern', 'classic']
// ]

array_combine() - Create Array Using Keys and Values

Creates an array by using one array for keys and another for values.

$keys = ['name', 'email', 'age'];
$values = ['John Doe', 'john@example.com', 30];

$combined = array_combine($keys, $values);
print_r($combined);
// ['name' => 'John Doe', 'email' => 'john@example.com', 'age' => 30]

array_replace() - Replace Array Values

Replaces values of an array with values from other arrays having the same keys.

$base = ['a' => 1, 'b' => 2, 'c' => 3];
$replacements = ['b' => 20, 'd' => 4];

$result = array_replace($base, $replacements);
print_r($result);  // ['a' => 1, 'b' => 20, 'c' => 3, 'd' => 4]

array_intersect_key() - Intersect by Keys

Returns an array containing all keys that exist in all compared arrays.

$array1 = ['a' => 1, 'b' => 2, 'c' => 3];
$array2 = ['a' => 4, 'c' => 5, 'd' => 6];

$intersection = array_intersect_key($array1, $array2);
print_r($intersection);  // ['a' => 1, 'c' => 3]

array_diff_key() - Difference by Keys

Returns an array containing all keys from the first array that are not in other arrays.

$array1 = ['a' => 1, 'b' => 2, 'c' => 3];
$array2 = ['a' => 4, 'c' => 5];

$diff = array_diff_key($array1, $array2);
print_r($diff);  // ['b' => 2]

array_pad() - Pad Array to Length

Pads an array to specified length with a given value.

$input = ['a', 'b', 'c'];

// Pad to length 5 with 'x'
$padded = array_pad($input, 5, 'x');
print_r($padded);  // ['a', 'b', 'c', 'x', 'x']

// Pad to the left (negative size)
$leftPadded = array_pad($input, -5, 'x');
print_r($leftPadded);  // ['x', 'x', 'a', 'b', 'c']

---

Array Sorting & Ordering

Functions for sorting arrays in various ways.

Basic Sorting Functions

sort() - Sort Indexed Array (Values)

Sorts an indexed array by values in ascending order.

$fruits = ['orange', 'apple', 'banana'];
sort($fruits);
print_r($fruits);  // ['apple', 'banana', 'orange']

$numbers = [3, 1, 4, 1, 5];
sort($numbers);
print_r($numbers);  // [1, 1, 3, 4, 5]

rsort() - Reverse Sort Indexed Array

Sorts an indexed array by values in descending order.

$numbers = [3, 1, 4, 1, 5];
rsort($numbers);
print_r($numbers);  // [5, 4, 3, 1, 1]

asort() - Sort Associative Array by Values

Sorts an associative array by values while maintaining key-value associations.

$ages = ['John' => 25, 'Jane' => 30, 'Bob' => 20];
asort($ages);
print_r($ages);  // ['Bob' => 20, 'John' => 25, 'Jane' => 30]

arsort() - Reverse Sort Associative Array by Values

Sorts an associative array by values in descending order.

$scores = ['Alice' => 95, 'Bob' => 87, 'Charlie' => 92];
arsort($scores);
print_r($scores);  // ['Alice' => 95, 'Charlie' => 92, 'Bob' => 87]

ksort() - Sort by Keys

Sorts an array by keys in ascending order.

$data = ['c' => 3, 'a' => 1, 'b' => 2];
ksort($data);
print_r($data);  // ['a' => 1, 'b' => 2, 'c' => 3]

krsort() - Reverse Sort by Keys

Sorts an array by keys in descending order.

$data = ['a' => 1, 'c' => 3, 'b' => 2];
krsort($data);
print_r($data);  // ['c' => 3, 'b' => 2, 'a' => 1]

Advanced Sorting Functions

usort() - Custom Sort by Values

Sorts by values using a user-defined comparison function.

$people = [
    ['name' => 'John', 'age' => 25],
    ['name' => 'Jane', 'age' => 30],
    ['name' => 'Bob', 'age' => 20]
];

// Sort by age
usort($people, function($a, $b) {
    return $a['age'] <=> $b['age'];  // PHP 7+ spaceship operator
});
print_r($people);  // Bob (20), John (25), Jane (30)

// Sort by name length
usort($people, function($a, $b) {
    return strlen($a['name']) <=> strlen($b['name']);
});

uasort() - Custom Sort Preserving Keys

Sorts by values using a user-defined function while preserving keys.

$students = [
    'student1' => ['name' => 'Alice', 'grade' => 85],
    'student2' => ['name' => 'Bob', 'grade' => 92],
    'student3' => ['name' => 'Charlie', 'grade' => 78]
];

uasort($students, function($a, $b) {
    return $b['grade'] <=> $a['grade'];  // Descending order
});
print_r($students);  // Keys preserved, sorted by grade

uksort() - Custom Sort by Keys

Sorts by keys using a user-defined comparison function.

$data = [
    'item_10' => 'Ten',
    'item_2' => 'Two',
    'item_1' => 'One'
];

uksort($data, function($a, $b) {
    // Extract numbers and compare numerically
    $numA = (int)str_replace('item_', '', $a);
    $numB = (int)str_replace('item_', '', $b);
    return $numA <=> $numB;
});
print_r($data);  // Sorted by numeric value in key

Multi-dimensional Array Sorting

array_multisort() - Sort Multiple Arrays

Sorts multiple arrays or multi-dimensional arrays.

$names = ['John', 'Jane', 'Bob'];
$ages = [25, 30, 20];

// Sort both arrays based on ages
array_multisort($ages, SORT_ASC, $names);
print_r($ages);   // [20, 25, 30]
print_r($names);  // ['Bob', 'John', 'Jane']

// Multi-dimensional array sorting
$people = [
    ['name' => 'John', 'age' => 25, 'salary' => 50000],
    ['name' => 'Jane', 'age' => 30, 'salary' => 60000],
    ['name' => 'Bob', 'age' => 25, 'salary' => 45000]
];

// Extract columns for sorting
$ages = array_column($people, 'age');
$salaries = array_column($people, 'salary');

// Sort by age (ascending), then by salary (descending)
array_multisort($ages, SORT_ASC, $salaries, SORT_DESC, $people);
print_r($people);

Sorting Options

$data = ['10', '2', '1', '20'];

// Default sort (lexicographic)
sort($data);
print_r($data);  // ['1', '10', '2', '20']

// Numeric sort
sort($data, SORT_NUMERIC);
print_r($data);  // ['1', '2', '10', '20']

// Case-insensitive string sort
$words = ['Banana', 'apple', 'Cherry'];
sort($words, SORT_STRING | SORT_FLAG_CASE);
print_r($words);  // ['apple', 'Banana', 'Cherry']

---

Practical Examples & Use Cases

Real-world examples demonstrating how to combine array functions effectively.

Example 1: User Management System

$users = [
    ['id' => 1, 'name' => 'John Doe', 'email' => 'john@example.com', 'age' => 25, 'active' => true],
    ['id' => 2, 'name' => 'Jane Smith', 'email' => 'jane@example.com', 'age' => 17, 'active' => true],
    ['id' => 3, 'name' => 'Bob Johnson', 'email' => 'bob@example.com', 'age' => 30, 'active' => false],
    ['id' => 4, 'name' => 'Alice Brown', 'email' => 'alice@example.com', 'age' => 28, 'active' => true]
];

// Get active adult users (age >= 18)
$activeAdults = array_filter($users, function($user) {
    return $user['age'] >= 18 && $user['active'];
});

// Sort by age (descending)
usort($activeAdults, function($a, $b) {
    return $b['age'] <=> $a['age'];
});

// Extract just names and emails
$contactInfo = array_map(function($user) {
    return ['name' => $user['name'], 'email' => $user['email']];
}, $activeAdults);

print_r($contactInfo);

Example 2: E-commerce Product Processing

$products = [
    ['name' => 'Laptop', 'category' => 'Electronics', 'price' => 999.99, 'stock' => 15],
    ['name' => 'Mouse', 'category' => 'Electronics', 'price' => 29.99, 'stock' => 0],
    ['name' => 'Desk', 'category' => 'Furniture', 'price' => 199.99, 'stock' => 8],
    ['name' => 'Chair', 'category' => 'Furniture', 'price' => 149.99, 'stock' => 12],
];

// Group products by category
$grouped = array_reduce($products, function($result, $product) {
    $result[$product['category']][] = $product;
    return $result;
}, []);

// Get available products (stock > 0) with discount
$availableProducts = array_map(function($product) {
    if ($product['stock'] > 0) {
        $product['discounted_price'] = round($product['price'] * 0.9, 2); // 10% discount
        return $product;
    }
    return null;
}, $products);

// Remove null values (out of stock items)
$availableProducts = array_filter($availableProducts);

// Sort by price (ascending)
usort($availableProducts, function($a, $b) {
    return $a['price'] <=> $b['price'];
});

Example 3: Data Processing Pipeline

$rawData = [
    'user1,John Doe,25,Engineer',
    'user2,Jane Smith,30,Designer',
    'user3,Bob Johnson,28,Developer',
    'user4,Alice Brown,32,Manager'
];

// Process CSV-like data
$processedUsers = array_map(function($line) {
    $parts = explode(',', $line);
    return [
        'id' => $parts[0],
        'name' => $parts[1],
        'age' => (int)$parts[2],
        'role' => $parts[3]
    ];
}, $rawData);

// Group by role
$roleGroups = array_reduce($processedUsers, function($groups, $user) {
    $groups[$user['role']][] = $user;
    return $groups;
}, []);

// Get average age per role
$roleAverages = array_map(function($users) {
    $ages = array_column($users, 'age');
    return round(array_sum($ages) / count($ages), 1);
}, $roleGroups);

print_r($roleAverages);

Example 4: Configuration Merging

// Default configuration
$defaultConfig = [
    'database' => [
        'host' => 'localhost',
        'port' => 3306,
        'charset' => 'utf8mb4'
    ],
    'cache' => [
        'enabled' => false,
        'ttl' => 3600
    ],
    'features' => ['logging', 'monitoring']
];

// User configuration
$userConfig = [
    'database' => [
        'host' => 'prod-db.example.com',
        'username' => 'app_user',
        'password' => 'secret123'
    ],
    'cache' => [
        'enabled' => true
    ],
    'features' => ['logging', 'analytics', 'debugging']
];

// Merge configurations recursively
$finalConfig = array_merge_recursive($defaultConfig, $userConfig);

// For features, we want unique values only
$finalConfig['features'] = array_unique($finalConfig['features']);

print_r($finalConfig);

Example 5: Statistics and Analysis

$salesData = [
    ['month' => 'Jan', 'revenue' => 12500, 'orders' => 45],
    ['month' => 'Feb', 'revenue' => 15800, 'orders' => 52],
    ['month' => 'Mar', 'revenue' => 18200, 'orders' => 63],
    ['month' => 'Apr', 'revenue' => 14300, 'orders' => 48],
    ['month' => 'May', 'revenue' => 21000, 'orders' => 71]
];

// Calculate total revenue
$totalRevenue = array_sum(array_column($salesData, 'revenue'));

// Calculate average revenue per month
$avgRevenue = $totalRevenue / count($salesData);

// Find month with highest revenue
$maxRevenueMonth = array_reduce($salesData, function($max, $current) {
    return (!$max || $current['revenue'] > $max['revenue']) ? $current : $max;
});

// Calculate revenue growth month-over-month
$growthData = [];
for ($i = 1; $i < count($salesData); $i++) {
    $current = $salesData[$i]['revenue'];
    $previous = $salesData[$i-1]['revenue'];
    $growth = round((($current - $previous) / $previous) * 100, 2);

    $growthData[] = [
        'month' => $salesData[$i]['month'],
        'growth_percent' => $growth
    ];
}

echo "Total Revenue: $" . number_format($totalRevenue) . "\n";
echo "Average Revenue: $" . number_format($avgRevenue) . "\n";
echo "Best Month: " . $maxRevenueMonth['month'] . " ($" .
     number_format($maxRevenueMonth['revenue']) . ")\n";

Performance Tips

// ✅ Efficient: Use array_column() for extracting data
$userIds = array_column($users, 'id');

// ❌ Less efficient: Manual loop
$userIds = [];
foreach ($users as $user) {
    $userIds[] = $user['id'];
}

// ✅ Efficient: Use array_key_exists() for null values
if (array_key_exists('optional_field', $data)) {
    // Handle the field
}

// ❌ Less reliable: Using isset() misses null values
if (isset($data['optional_field'])) {
    // This won't work if the value is null
}

// ✅ Efficient: Chain operations
$result = array_unique(
    array_filter(
        array_map('trim', $inputArray),
        'strlen'
    )
);