PHP Fundamentals

Array Functions

13 min Lesson 13 of 45

Mastering PHP Array Functions

PHP provides over 70 built-in array functions that make working with arrays powerful and efficient. In this lesson, we'll explore the most useful and commonly used array functions that every PHP developer should know.

Note: Most array functions either modify the original array in place or return a new array. Always check the function documentation to understand its behavior.

Array Transformation Functions

array_map() - Transform Elements

Apply a callback function to each element:

<?php // Square all numbers $numbers = [1, 2, 3, 4, 5]; $squared = array_map(function($n) { return $n * $n; }, $numbers); print_r($squared); // [1, 4, 9, 16, 25] // Convert to uppercase $names = ["alice", "bob", "charlie"]; $upper = array_map("strtoupper", $names); print_r($upper); // ["ALICE", "BOB", "CHARLIE"] // Multiple arrays $first = [1, 2, 3]; $second = [10, 20, 30]; $result = array_map(function($a, $b) { return $a + $b; }, $first, $second); print_r($result); // [11, 22, 33] ?>

array_filter() - Filter Elements

Filter array elements using a callback:

<?php // Filter even numbers $numbers = [1, 2, 3, 4, 5, 6, 7, 8]; $even = array_filter($numbers, function($n) { return $n % 2 === 0; }); print_r($even); // [2, 4, 6, 8] // Filter non-empty values $data = ["apple", "", "banana", null, "cherry", 0]; $filtered = array_filter($data); print_r($filtered); // ["apple", "banana", "cherry"] // Filter with keys $ages = ["John" => 25, "Jane" => 30, "Bob" => 17, "Alice" => 22]; $adults = array_filter($ages, function($age, $name) { return $age >= 18; }, ARRAY_FILTER_USE_BOTH); print_r($adults); ?>

array_reduce() - Reduce to Single Value

Reduce array to a single value using a callback:

<?php // Sum all numbers $numbers = [1, 2, 3, 4, 5]; $sum = array_reduce($numbers, function($carry, $item) { return $carry + $item; }, 0); echo $sum; // 15 // Find maximum $max = array_reduce($numbers, function($carry, $item) { return $item > $carry ? $item : $carry; }, $numbers[0]); echo $max; // 5 // Concatenate strings $words = ["Hello", "World", "PHP"]; $sentence = array_reduce($words, function($carry, $item) { return $carry . " " . $item; }, ""); echo trim($sentence); // "Hello World PHP" ?>
Tip: array_map(), array_filter(), and array_reduce() are fundamental functional programming patterns. Master them for cleaner, more expressive code.

Array Searching Functions

in_array() - Check if Value Exists

<?php $fruits = ["apple", "banana", "cherry"]; if (in_array("banana", $fruits)) { echo "Found banana!"; } // Strict type checking $numbers = [1, 2, 3, "4"]; var_dump(in_array(4, $numbers)); // true (loose) var_dump(in_array(4, $numbers, true)); // false (strict) ?>

array_search() - Find Key of Value

<?php $colors = ["red", "green", "blue", "yellow"]; $key = array_search("blue", $colors); echo $key; // 2 // Returns false if not found $key = array_search("purple", $colors); if ($key === false) { echo "Color not found"; } // With associative arrays $ages = ["John" => 25, "Jane" => 30, "Bob" => 25]; $name = array_search(25, $ages); echo $name; // "John" (first match) ?>

array_key_exists() vs isset()

<?php $data = ["name" => "John", "age" => null]; // array_key_exists checks if key exists (even if value is null) var_dump(array_key_exists("age", $data)); // true var_dump(array_key_exists("email", $data)); // false // isset returns false if value is null var_dump(isset($data["age"])); // false var_dump(isset($data["name"])); // true ?>
Warning: Use array_search() with strict comparison (===) because it returns the key (which could be 0), not true/false.

Array Manipulation Functions

array_slice() - Extract Portion

<?php $fruits = ["apple", "banana", "cherry", "date", "elderberry"]; // Get slice from position 1, length 3 $slice = array_slice($fruits, 1, 3); print_r($slice); // ["banana", "cherry", "date"] // Negative offset (from end) $slice = array_slice($fruits, -2); print_r($slice); // ["date", "elderberry"] // Preserve keys $slice = array_slice($fruits, 1, 3, true); print_r($slice); ?>

array_splice() - Remove and Replace

<?php $colors = ["red", "green", "blue", "yellow"]; // Remove 2 elements starting at index 1 $removed = array_splice($colors, 1, 2); print_r($removed); // ["green", "blue"] print_r($colors); // ["red", "yellow"] // Remove and replace $colors = ["red", "green", "blue", "yellow"]; array_splice($colors, 1, 2, ["orange", "purple"]); print_r($colors); // ["red", "orange", "purple", "yellow"] // Insert without removing $colors = ["red", "blue"]; array_splice($colors, 1, 0, ["green"]); print_r($colors); // ["red", "green", "blue"] ?>

array_merge() - Combine Arrays

<?php // Merge indexed arrays $arr1 = [1, 2, 3]; $arr2 = [4, 5, 6]; $merged = array_merge($arr1, $arr2); print_r($merged); // [1, 2, 3, 4, 5, 6] // Merge associative arrays (later values override) $default = ["color" => "red", "size" => "M"]; $custom = ["size" => "L", "style" => "casual"]; $config = array_merge($default, $custom); print_r($config); // ["color" => "red", "size" => "L", "style" => "casual"] // Merge multiple arrays $result = array_merge($arr1, $arr2, [7, 8, 9]); print_r($result); ?>

Array Calculation Functions

<?php $numbers = [10, 20, 30, 40, 50]; // Sum of all elements echo array_sum($numbers); // 150 // Product of all elements echo array_product($numbers); // 12000000 // Count elements echo count($numbers); // 5 // Count element frequencies $items = ["apple", "banana", "apple", "cherry", "banana", "apple"]; $counts = array_count_values($items); print_r($counts); // ["apple" => 3, "banana" => 2, "cherry" => 1] ?>

Array Sorting Functions

<?php // Sort indexed array (values) $numbers = [3, 1, 4, 1, 5, 9, 2, 6]; sort($numbers); // Ascending print_r($numbers); rsort($numbers); // Descending print_r($numbers); // Sort associative array (by value, maintain keys) $ages = ["John" => 25, "Jane" => 30, "Bob" => 20]; asort($ages); // Ascending by value print_r($ages); arsort($ages); // Descending by value print_r($ages); // Sort associative array (by key) ksort($ages); // Ascending by key print_r($ages); krsort($ages); // Descending by key print_r($ages); // Custom sorting with callback $words = ["apple", "Banana", "cherry", "Date"]; usort($words, function($a, $b) { return strcasecmp($a, $b); // Case-insensitive }); print_r($words); ?>
Note: Sorting functions modify the original array and return true/false (not a sorted copy).

Array Combination Functions

<?php // Combine two arrays as keys and values $keys = ["name", "age", "city"]; $values = ["John", 25, "New York"]; $person = array_combine($keys, $values); print_r($person); // ["name" => "John", "age" => 25, "city" => "New York"] // Chunk array into smaller arrays $numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]; $chunks = array_chunk($numbers, 3); print_r($chunks); // [[1, 2, 3], [4, 5, 6], [7, 8, 9]] // Fill array with values $filled = array_fill(0, 5, "x"); print_r($filled); // ["x", "x", "x", "x", "x"] // Fill with range of values $range = range(1, 10, 2); print_r($range); // [1, 3, 5, 7, 9] ?>

Array Unique and Difference Functions

<?php // Remove duplicates $numbers = [1, 2, 2, 3, 4, 4, 5]; $unique = array_unique($numbers); print_r($unique); // [1, 2, 3, 4, 5] // Find values in first array not in second $arr1 = [1, 2, 3, 4, 5]; $arr2 = [3, 4, 5, 6, 7]; $diff = array_diff($arr1, $arr2); print_r($diff); // [1, 2] // Find common values $intersect = array_intersect($arr1, $arr2); print_r($intersect); // [3, 4, 5] // Difference by keys $a = ["a" => 1, "b" => 2, "c" => 3]; $b = ["b" => 2, "c" => 4, "d" => 5]; $diff = array_diff_key($a, $b); print_r($diff); // ["a" => 1] ?>

Array Reversal and Shuffling

<?php // Reverse array order $colors = ["red", "green", "blue"]; $reversed = array_reverse($colors); print_r($reversed); // ["blue", "green", "red"] // Flip keys and values $map = ["a" => 1, "b" => 2, "c" => 3]; $flipped = array_flip($map); print_r($flipped); // [1 => "a", 2 => "b", 3 => "c"] // Shuffle array (randomize order) $deck = ["A", "K", "Q", "J", "10"]; shuffle($deck); print_r($deck); // Random order // Get random element(s) $fruits = ["apple", "banana", "cherry", "date"]; $random = array_rand($fruits, 2); print_r($random); // Two random keys ?>

Practical Example: Data Processing Pipeline

<?php // Process user data $users = [ ["name" => "John Doe", "age" => 25, "active" => true], ["name" => "Jane Smith", "age" => 17, "active" => true], ["name" => "Bob Johnson", "age" => 35, "active" => false], ["name" => "Alice Brown", "age" => 28, "active" => true] ]; // Filter: Get active adult users $activeAdults = array_filter($users, function($user) { return $user["active"] && $user["age"] >= 18; }); // Map: Extract names $names = array_map(function($user) { return $user["name"]; }, $activeAdults); // Reduce: Create comma-separated list $nameList = array_reduce($names, function($carry, $name) { return $carry ? $carry . ", " . $name : $name; }, ""); echo "Active adult users: $nameList"; // Output: Active adult users: John Doe, Alice Brown ?>

Practical Example: Shopping Cart Operations

<?php $cart = [ ["id" => 1, "name" => "Laptop", "price" => 999, "qty" => 1], ["id" => 2, "name" => "Mouse", "price" => 25, "qty" => 2], ["id" => 3, "name" => "Keyboard", "price" => 75, "qty" => 1] ]; // Calculate subtotals $cartWithSubtotals = array_map(function($item) { $item["subtotal"] = $item["price"] * $item["qty"]; return $item; }, $cart); // Calculate total $total = array_reduce($cartWithSubtotals, function($sum, $item) { return $sum + $item["subtotal"]; }, 0); echo "Cart Total: $$total"; // Cart Total: $1124 // Find specific item $itemKey = array_search(2, array_column($cart, "id")); if ($itemKey !== false) { echo "Found: " . $cart[$itemKey]["name"]; } // Sort by price usort($cart, function($a, $b) { return $a["price"] - $b["price"]; }); ?>
Exercise:
  1. Create an array of numbers and use array functions to:
    • Filter only even numbers
    • Square each number
    • Calculate the sum of all squared even numbers
  2. Create an array of students with name, grade, and subject. Write code to:
    • Filter students with grades above 80
    • Sort them by grade descending
    • Extract only their names
  3. Create two arrays and find their union, intersection, and difference
  4. Write a function that removes duplicate values from a nested array

Performance Tips

  • Use isset() instead of array_key_exists() when null values aren't important (it's faster)
  • Use array_map() instead of foreach loops when transforming all elements
  • Avoid array_merge() in loops; use array_push() or [] instead
  • Use array_column() to extract a single column from multi-dimensional arrays
  • Chain array functions for cleaner, more readable code
Tip: Learn to think functionally with array_map(), array_filter(), and array_reduce(). They often lead to cleaner, more maintainable code than traditional loops.

Common Patterns

<?php // Extract column from 2D array $users = [ ["name" => "John", "email" => "john@example.com"], ["name" => "Jane", "email" => "jane@example.com"] ]; $emails = array_column($users, "email"); // Pluck with keys $emailMap = array_column($users, "email", "name"); print_r($emailMap); // ["John" => "john@example.com", "Jane" => "jane@example.com"] // Group by key $items = [ ["category" => "fruit", "name" => "apple"], ["category" => "fruit", "name" => "banana"], ["category" => "veggie", "name" => "carrot"] ]; $grouped = []; foreach ($items as $item) { $grouped[$item["category"]][] = $item["name"]; } print_r($grouped); ?>

Summary

In this lesson, you learned:

  • Transformation functions: array_map(), array_filter(), array_reduce()
  • Search functions: in_array(), array_search(), array_key_exists()
  • Manipulation functions: array_slice(), array_splice(), array_merge()
  • Calculation functions: array_sum(), array_product(), count()
  • Set operations: array_unique(), array_diff(), array_intersect()
  • Practical applications in data processing and business logic

Mastering array functions is essential for writing efficient, clean PHP code. Practice combining them to solve complex problems elegantly!

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