PHP array_filter: How to Filter Array Values with Examples

You can use array_filter in PHP to remove unwanted data from arrays. It works with a custom callback or default rules.

Understand the array_filter Function in PHP

The array_filter function removes elements from an array based on a given test. This function checks each element and keeps only those that pass the test.

Here is the basic syntax:

$result = array_filter($array, callback, mode);

• $array: the source array.
• callback: optional callable to test each value.
• mode: optional flag to pass keys as well.

The array_filter keeps the original keys by default, while the filtered array will have the same keys as the source array.

A callback is a function you pass to array_filter. PHP calls it on each element and expects it to return true for values to keep and false for values to remove.

The array_filter removes all elements that evaluate to false without a callback.

Here is an example:

function isEven($num) {
  return $num % 2 === 0;
}

The common cases:

• Developers use array_filter for data validation to clean arrays.
• You can remove null values or false entries. Also, allows you to ignore empty strings or keep specific matches based on rules.

You can also use anonymous functions inside array_filter for inline tests. This avoids the need for separate named functions.

Here is an example:

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

$result = array_filter($nums, function($value) { 
   return $value > 3;
}); 

print_r($result);

This keeps numbers greater than 3. Here is the output:

Array
(
    [3] => 4
    [4] => 5
)

Use the array_filter with associative arrays

The array_filter works with associative arrays just like with indexed arrays. You can also pass the ARRAY_FILTER_USE_KEY flag to filter by keys.

For example:

$users = [ 'david' => 25, 'hala' => 17, 'carol' => 30 ]; 

$adults = array_filter($users, function($age) {  
  return $age >= 18;
}); 

print_r($adults);

This keeps users with an age of 18 or older. The output:

Array
(
    [david] => 25
    [carol] => 30
)

Here is another example with mode ARRAY_FILTER_USE_KEY:

$data = [ 'first' => 10, 'second' => 20, 'third' => 5 ]; 

$result = array_filter($data, function($key) {  
  return $key !== 'second';
}, ARRAY_FILTER_USE_KEY); 

print_r($result);

This keeps all items except the one with the key second. Here is the output:

Array
(
    [first] => 10
    [third] => 5
)

Examples of array_filter in PHP

Filter Odd Numbers:

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

$odds = array_filter($nums, function($value) { 
  return $value % 2 === 1; 
}); 

print_r($odds);

This keeps values that return a remainder of 1 when divided by 2. The output:

Array
(
    [0] => 1
    [2] => 3
    [4] => 5
)

Remove Empty Values from Array:

$items = ['apple', '', 'banana', null, 'cherry']; 
$result = array_filter($items); 
print_r($result);

This removes all empty or null values and keeps only valid strings. Here is the output:

Array
(
    [0] => apple
    [2] => banana
    [4] => cherry
)

Filter by Both Keys and Values:

$records = [ 'user1' => 100, 'user2' => 50, 'admin' => 200 ]; 

$result = array_filter($records, function($value, $key) { 
  return $value > 80 && $key !== 'admin'; 
}, ARRAY_FILTER_USE_BOTH); 

print_r($result);

This keeps users with scores above 80 but excludes the admin:

Array
(
    [user1] => 100
)

Advanced Filtering with External Data:

$allowed = ['a', 'c']; 

$data = [ 'a' => 10, 'b' => 20, 'c' => 30 ]; 

$result = array_filter($data, function($key) use ($allowed) { 
  return in_array($key, $allowed); 
}, ARRAY_FILTER_USE_KEY); 

print_r($result);

This keeps only the keys listed in the $allowed array:

Array
(
    [a] => 10
    [c] => 30
)

Wrapping Up

In this article, you learned how to use array_filter with callbacks and default rules. You also saw how to handle associative arrays and keep keys intact.

Here is a quick recap:

• array_filter removes unwanted values.
• Works with callbacks or default rules.
• Supports associative arrays.
• Keeps original keys.

FAQs

$result = array_filter($data, function($value) {
    return $value > 1;
});

$data = [0, 1, false, 2, '', 3];
$result = array_filter($data, function($value) {
    return $value > 3;
});
print_r($result);

$data = ["a" => 1, "b" => 2, "c" => 3]; 
$result = array_filter($data, function($value) {
    return $value > 3;
});
print_r($result);

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