Syntax
The syntax of the array_filter() function is:
array array_filter(array $array, callable|null $callback = null, int $mode = 0)
Here,
- $array: The input array that needs to be filtered.
- $callback: (Optional) A function that decides whether an element should be kept or removed.
- $mode: (Optional) Defines whether to pass only values or both keys and values to the callback function.
If no callback function is provided, array_filter() removes all elements that evaluate to false (such as 0, null, false, and empty strings).
Parameters
- $array (Required) – The input array from which elements will be filtered.
- $callback (Optional) – A function that determines whether an element should be included in the result. If null, the function removes all elements that evaluate to false.
- $mode (Optional, Default = 0) – Specifies how the callback function will be used:
- 0 (default) – Only values are passed to the callback function.
- ARRAY_FILTER_USE_KEY – Only array keys are passed to the callback function.
- ARRAY_FILTER_USE_BOTH – Both keys and values are passed to the callback function.
Return Value
The array_filter() function returns a new array containing elements that satisfy the condition defined in the callback function. The array keys are preserved but not reindexed.
Examples
Example 1: Filtering Even Numbers
function isEven($num) {
return $num % 2 == 0;
}
$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
$evenNumbers = array_filter($numbers, "isEven");
print_r($evenNumbers);
You can also try this code with Online PHP Compiler
Output:
Array
(
[1] => 2
[3] => 4
[5] => 6
[7] => 8
[9] => 10
)
Example 2: Removing Empty Strings
$strings = ["Hello", "", "PHP", " ", "World", null, "!"];
$filteredStrings = array_filter($strings);
print_r($filteredStrings);
You can also try this code with Online PHP Compiler
Output:
Array
(
[0] => Hello
[2] => PHP
[4] => World
[6] => !
)
Example 3: Using the `$mode` Parameter
The `$mode` parameter allows you to pass both the key & value to the callback function. Let’s see how you can use it:
<?php
$associativeArray = [
'a' => 1,
'b' => 0,
'c' => 3,
'd' => '',
'e' => 5
];
// Callback function to filter based on both key and value
function filterKeyValue($value, $key) {
return $value !== '' && $key !== 'b';
}
// Filter the array with ARRAY_FILTER_USE_BOTH flag
$filteredArray = array_filter($associativeArray, 'filterKeyValue', ARRAY_FILTER_USE_BOTH);
// Print the result
print_r($filteredArray);
?>
You can also try this code with Online PHP Compiler
Output:
Array
(
[a] => 1
[c] => 3
[e] => 5
)
Example 4: Filtering Without a Callback
If you don’t provide a callback function, `array_filter()` removes all "falsey" values from the array. For example:
<?php
$mixedValues = [0, 1, false, 2, '', 3, null, 4, '0', 5];
// Filter the array without a callback
$filteredValues = array_filter($mixedValues);
// Print the result
print_r($filteredValues);
?>
You can also try this code with Online PHP Compiler
Output:
Array
(
[1] => 1
[3] => 2
[5] => 3
[7] => 4
[9] => 5
)
In this case, all "falsey" values like `0`, `false`, `""`, `null`, & `'0'` are removed from the array.
Here, the callback function filters out elements where the value is an empty string or the key is `'b'`.
Example 5: Using ARRAY_FILTER_USE_KEY
$array = [
"a" => 10,
"b" => 20,
"c" => 30
];
$filteredKeys = array_filter($array, function ($key) {
return $key !== "b";
}, ARRAY_FILTER_USE_KEY);
print_r($filteredKeys);
You can also try this code with Online PHP Compiler
Output:
Array
(
[a] => 10
[c] => 30
)
Common Use Cases and Best Practices for `array_filter()`
The `array_filter()` function is versatile & can be used in various scenarios to make your code cleaner & more efficient.
Now let’s discuss some of the common use cases & best practices to help you get the most out of this function.
Use Case 1: Filtering Data from User Input
When working with user input, you often need to sanitize or filter data. For example, you might want to remove empty values from a form submission.
<?php
// Simulated user input from a form
$userInput = [
'name' => 'John Doe',
'email' => '',
'age' => '25',
'city' => null,
'country' => 'USA'
];
// Filter out empty values
$filteredInput = array_filter($userInput);
// Print the result
print_r($filteredInput);
?>
You can also try this code with Online PHP Compiler
Output:
Array
(
[name] => John Doe
[age] => 25
[country] => USA
)
In this example, `array_filter()` removes empty values like `""` & `null`, ensuring only valid data is processed.
Use Case 2: Filtering Associative Arrays
You can use `array_filter()` to filter associative arrays based on specific conditions. For instance, let’s filter an array of products to find items with a price greater than 50.
<?php
$products = [
['name' => 'Laptop', 'price' => 1200],
['name' => 'Mouse', 'price' => 25],
['name' => 'Keyboard', 'price' => 60],
['name' => 'Monitor', 'price' => 300]
];
// Callback function to filter products with price > 50
function filterExpensiveProducts($product) {
return $product['price'] > 50;
}
// Filter the array
$expensiveProducts = array_filter($products, 'filterExpensiveProducts');
// Print the result
print_r($expensiveProducts);
?>
You can also try this code with Online PHP Compiler
Output:
Array
(
[0] => Array
(
[name] => Laptop
[price] => 1200
)
[2] => Array
(
[name] => Keyboard
[price] => 60
)
[3] => Array
(
[name] => Monitor
[price] => 300
)
)
Here, the callback function checks if the product price is greater than 50, & `array_filter()` returns only those products.
Use Case 3: Combining `array_filter()` with Other Array Functions
You can combine `array_filter()` with other array functions like `array_map()` or `array_reduce()` for more complex operations. For example, let’s filter an array of numbers & then calculate their sum.
<?php
$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
// Filter out even numbers
$oddNumbers = array_filter($numbers, function($number) {
return $number % 2 !== 0;
});
// Calculate the sum of odd numbers
$sum = array_reduce($oddNumbers, function($carry, $number) {
return $carry + $number;
}, 0);
// Print the result
echo "Sum of odd numbers: $sum";
?>
You can also try this code with Online PHP Compiler
Output:
Sum of odd numbers: 25
In this example, `array_filter()` removes even numbers, & `array_reduce()` calculates the sum of the remaining odd numbers.
Best Practices
1. Use Anonymous Functions for Simple Filters: If the filtering logic is simple, use anonymous functions (closures) instead of defining a separate function. This keeps your code concise.
$filteredArray = array_filter($array, function($value) {
return $value > 10;
});
2. Preserve Keys When Needed: By default, `array_filter()` preserves the keys of the original array. If you want to reindex the array, use `array_values()` after filtering.
$filteredArray = array_values(array_filter($array));
3. Combine with Other Array Functions: As shown earlier, combining `array_filter()` with functions like `array_map()` or `array_reduce()` can help you perform complex operations efficiently.
PHP Version
The array_filter() function has been available since PHP 4.0.6 and is supported in all modern PHP versions, including PHP 5, PHP 7, and PHP 8.
PHP Changelog
- PHP 5.6.0 – Added the $mode parameter.
- PHP 4.0.6 – Initial introduction of array_filter() function.
Frequently Asked Questions
What happens if no callback function is provided?
If no callback function is provided, array_filter() will remove all elements that evaluate to false (0, false, null, "", etc.).
Does array_filter() reindex the array?
No, array_filter() preserves the original keys. If needed, you can use array_values() to reset the keys.
Can array_filter() be used with associative arrays?
Yes, array_filter() works with both indexed and associative arrays.
Conclusion
In this article, we learned about the PHP array_filter() function, which helps filter elements of an array using a callback function. This function is useful for removing unwanted values and processing data efficiently. Understanding how to use array_filter() allows developers to write cleaner and more optimized code, improving both performance and readability in PHP applications.
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