Why array functions matter in PHP - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array_map with anonymous function

What is the output of this PHP code?

PHP

<?php
$numbers = [1, 2, 3, 4];
$result = array_map(fn($n) => $n * 2, $numbers);
print_r($result);
?>

A Array ( [0] => 2 [1] => 4 [2] => 6 [3] => 8 )

B Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 )

C Array ( [0] => 1 [1] => 4 [2] => 9 [3] => 16 )

D Syntax error

💡 Hint

array_map applies the function to each element in the array.

array_map applies the function fn($n) => $n * 2 to each element, doubling each number.

❓ Predict Output

intermediate

Result of array_filter with callback

What does this PHP code output?

PHP

<?php
$values = [10, 15, 20, 25, 30];
$filtered = array_filter($values, fn($v) => $v > 20);
print_r($filtered);
?>

A Array ( [0] => 10 [1] => 15 [2] => 20 )

B Fatal error: Uncaught TypeError

C Array ( [0] => 10 [1] => 15 [2] => 20 [3] => 25 [4] => 30 )

D Array ( [3] => 25 [4] => 30 )

💡 Hint

array_filter keeps elements where the callback returns true.

Only values greater than 20 (25 and 30) remain in the filtered array, keys preserved.

🔧 Debug

advanced

Output of array_reduce without initial value

This PHP code is intended to sum all numbers in the array. What is the output?

PHP

<?php
$nums = [1, 2, 3, 4];
$sum = array_reduce($nums, fn($carry, $item) => $carry + $item);
echo $sum;
?>

A Fatal error: Uncaught TypeError

B Notice: Undefined variable: carry

C Output: 10

D Warning: array_reduce() expects parameter 3 to be mixed, none given

💡 Hint

array_reduce uses the first element as the initial carry when not specified and the array is not empty.

No error is produced. The first element (1) is used as the initial value for $carry, and the function sums the elements: 1+2+3+4=10. Providing an explicit initial value (like 0) is recommended for robustness, especially with empty arrays.

❓ Predict Output

advanced

Output of array_column with associative arrays

What is the output of this PHP code?

PHP

<?php
$data = [
  ['id' => 1, 'name' => 'Alice'],
  ['id' => 2, 'name' => 'Bob'],
  ['id' => 3, 'name' => 'Charlie']
];
$names = array_column($data, 'name');
print_r($names);
?>

A Array ( [0] => Alice [1] => Bob [2] => Charlie )

B Array ( [1] => Alice [2] => Bob [3] => Charlie )

C Syntax error

D Array ( [id] => name )

💡 Hint

array_column extracts values from a specific key in each sub-array.

array_column returns a simple array of the 'name' values preserving numeric keys starting at 0.

🧠 Conceptual

expert

Why use array functions instead of loops?

Which of the following is the best reason to prefer PHP array functions like array_map, array_filter, and array_reduce over manual loops?

A They allow modifying the original array without copying

B They provide clearer, shorter code that expresses intent and reduces errors

C They always run faster than loops in every situation

D They automatically parallelize code for better performance

💡 Hint

Think about code readability and maintenance.

Array functions make code easier to read and less error-prone by expressing what you want to do, not how.