What Are The Differences Between Array_map, Array_walk And Array_filter in PHP?

Core Functionality of Array_map

Array_map is a PHP function that applies a callback function to each element of one or more arrays. It transforms array elements without changing the original array. Array_map returns a new array with the results of applying the callback function to each element. This function can work with multiple input arrays, allowing you to perform operations on corresponding elements from different arrays.

$numbers = [1, 2, 3, 4, 5];
$squared = array_map(function($n) {
    return $n * $n;
}, $numbers);
// $squared now contains [1, 4, 9, 16, 25]

Key Features of Array_walk

Array_walk iterates over each element of an array and applies a user-defined callback function. Unlike array_map, array_walk can modify the original array directly. This function is useful for operations that require in-place modifications of array elements. Array_walk provides access to both the array keys and values in the callback function, allowing for operations based on the array structure.

Main Characteristics of Array_filter

Array_filter filters elements of an array based on a specified condition. It creates a new array containing only the elements that meet a given criteria. The function applies a callback function to each element of the input array, and if the callback returns true, the element is included in the resulting array. Array_filter keeps the original keys of the array elements that pass the filter, which can be useful for maintaining the original array structure in the filtered result.

Modifying Array Values

Array_map creates a new array with the results of applying the callback function to each element. It does not change the original array. Array_walk can modify the input array directly. It lets you change the values of the original array within the callback function. Array_filter selects elements based on a condition without modifying values.

Handling Array Keys

Array_map only passes the values to the callback function, not the keys. Array_walk provides access to both keys and values in its callback function. Array_filter keeps the original keys of the elements that pass the filter condition in the output array.

Return Values and Array Lengths

Array_map returns a new array with the same length as the input array (or the longest input array if multiple arrays are provided). The returned array contains the results of applying the callback function to each element. Array_walk returns a boolean value (true) after processing the array, not a new array. Array_filter returns a new array with a subset of elements from the original array that meet the filtering condition. The length of this new array depends on how many elements pass the filter.

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

// Array_map example
$doubled = array_map(function($n) {
    return $n * 2;
}, $numbers);
// $doubled is [2, 4, 6, 8, 10]

// Array_walk example
array_walk($numbers, function(&$value, $key) {
    $value *= 2;
});
// $numbers is now [2, 4, 6, 8, 10]

// Array_filter example
$even = array_filter($numbers, function($n) {
    return $n % 2 == 0;
});
// $even is [1 => 4, 3 => 8]

Using Array_map for Data Transformation

Array_map transforms all elements in an array without changing the original array. Here's an example:

$numbers = [1, 2, 3, 4, 5];
$squared = array_map(function($n) {
    return $n * $n;
}, $numbers);
// $squared is [1, 4, 9, 16, 25]

Array_map can work with multiple input arrays:

$first_names = ['John', 'Jane', 'Mike'];
$last_names = ['Doe', 'Smith', 'Johnson'];
$full_names = array_map(function($first, $last) {
    return $first . ' ' . $last;
}, $first_names, $last_names);
// $full_names is ['John Doe', 'Jane Smith', 'Mike Johnson']

$strings = ['hello', 'world', 'php'];
$uppercase = array_map('strtoupper', $strings);
// $uppercase is ['HELLO', 'WORLD', 'PHP']

Implementing Array_walk for In-Place Modifications

Array_walk modifies array elements directly. Here's an example:

$fruits = ['apple', 'banana', 'cherry'];
array_walk($fruits, function(&$value, $key) {
    $value = ucfirst($value);
});
// $fruits is now ['Apple', 'Banana', 'Cherry']

You can access and use array keys with array_walk:

$prices = ['apple' => 0.5, 'banana' => 0.7, 'cherry' => 1.2];
array_walk($prices, function(&$value, $key) {
    echo "The price of $key is $value\n";
    $value *= 1.1; // Increase price by 10%
});
// Outputs price information and updates $prices

$nested = [
    'fruits' => ['apple', 'banana'],
    'vegetables' => ['carrot', 'tomato']
];
array_walk_recursive($nested, function(&$value) {
    $value = strtoupper($value);
});
// $nested now contains uppercase values in all levels

Applying Array_filter for Data Selection

Array_filter selects elements based on a condition. Here's an example:

$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
$even_numbers = array_filter($numbers, function($n) {
    return $n % 2 == 0;
});
// $even_numbers is [1 => 2, 3 => 4, 5 => 6, 7 => 8, 9 => 10]

This example shows how array_filter keeps the original keys in the filtered result:

$grades = ['Math' => 85, 'English' => 78, 'Science' => 92, 'History' => 64];
$high_grades = array_filter($grades, function($grade) {
    return $grade >= 80;
});
// $high_grades is ['Math' => 85, 'Science' => 92]

$mixed = [0, null, '', false, 1, 'hello', []];
$non_empty = array_filter($mixed);
// $non_empty is [4 => 1, 5 => 'hello']

These examples show how array_map, array_walk, and array_filter can be used for different array operations in PHP, each with its own strengths and uses.