array_filter is used to filter elements in an array that meet the criteria. It is useful when you need to filter null values, specific values, or filter by rules, such as string length, such as removing false values, retaining even numbers, or long strings. When using it, you can choose whether to pass the callback function: if you do not pass, false values ??such as false, null will be automatically filtered; if you pass, it will return true or false according to the callback, it will decide whether to retain or not. In addition, the ARRAY_FILTER_USE_BOTH parameter can be filtered in conjunction with the key name, and the index can be reset using array_values.
PHP's array_filter function is a very practical tool for filtering elements in an array. It can keep only the values ??that meet the conditions according to the conditions you define, thereby simplifying the data processing process.
When to use array_filter?
When you need to filter out data that meets certain conditions from an array, you can use array_filter . for example:
- Remove null or invalid data
- Filter values ??greater than a certain number
- Filter according to string length, type, or other rules
It does not modify the original array, but returns a new filtered array.
The most basic usage
The simplest form is to filter out "falsy values" without passing a callback function:
$numbers = [0, 1, null, '', 3, false, 5]; $result = array_filter($numbers); // Output: [1, 3, 5]
The above example will automatically remove 0 , null , empty strings and false . If you just want to remove null or empty strings, you have to write the callback function yourself.
Custom filtering logic
You can define your own filtering rules by passing in a callback function. For example, only even numbers are preserved:
$numbers = [1, 2, 3, 4, 5, 6];
$even = array_filter($numbers, function($num) {
return $num % 2 === 0;
});
// Output: [2, 4, 6] Returning true in the callback function means that the element is retained, and returning false will be filtered out.
It can also be used to filter strings, such as finding words with length greater than 3:
$words = ['cat', 'apple', 'dog', 'banana'];
$longWords = array_filter($words, function($word) {
return strlen($word) > 3;
});
// Output: ['apple', 'banana']Notes and tips
- Reserved key name : By default,
array_filterretains the key name of the original array. If you want to reset the index, you can use it witharray_values(). - Callback processing with key names : If you want to filter based on key, you can use two parameters in the callback function:
$array = ['a' => 10, 'b' => 20, 'c' => 5];
$result = array_filter($array, function($value, $key) {
return $key !== 'b';
}, ARRAY_FILTER_USE_BOTH);This way, you can use value and key to determine whether elements are retained.
- Multidimensional arrays are also applicable : as long as the child elements are accessed correctly in the callback.
Basically that's it. Mastering array_filter can make you more concise and efficient when processing arrays.
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