Among the few features that got added to the latest released version of PHP 7, the arrow function feature seems to be amazing to me since it has been in JS ES6. So I decided to talk about it using some common Higher Order Functions we already know — array_map() and array_filter.
Let us take a look on how this is used in the previous versions of PHP before PHP 7.4. You would see the need to leverage PHP 7.4 to make things lot easier and cleaner. Yes! Cleaner
This is the regular
way we write the php and use array_filter() function before PHP 7.4
Now let’s look at what PHP 7.4 brings to the table with same example of code above:
Did you notice how 3 lines of code got reduced to 1 in line 4–6 and line 4 of the two examples above respectively and same result is being produced?
Did you also noticed the weird fn
keyword in the second example? Well, it means function. And yes there is an implicit return with the arrow function.
PHP 7.4 makes writing the same piece of code cleaner and faster with arrow function feature.
(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)
array_filter — Filters elements of an array using a callback function
Description
array_filter(array $array,
?callable $callback = null, int $mode = 0): array
Array keys are preserved, and may result in gaps if the array was indexed. The result array can be reindexed using the array_values() function.
Parameters
array The array to iterate over
callback The callback function to use
If no callback is supplied, all empty entries of array will be removed. See empty() for how PHP defines empty in this case.
mode Flag determining what arguments are sent to callback:
-
ARRAY_FILTER_USE_KEY - pass key as the only argument to callback instead of the value -
ARRAY_FILTER_USE_BOTH - pass both value and key as arguments to callback instead of the value
Default is 0 which will pass value
as the only argument to callback instead. Return Values
Returns the filtered array.
Changelog
| Version | Description |
|---|
| 8.0.0
| callback is nullable now.
|
| 8.0.0
| If callback expects a parameter to be passed by reference, this function will now emit an E_WARNING.
|
Examples
Example #1 array_filter() example
<?php
function odd($var)
{
// returns whether the input integer is odd
return $var & 1;
}
function
even($var)
{
// returns whether the input integer is even
return !($var & 1);
}$array1 = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5];
$array2 = [6, 7, 8, 9, 10, 11, 12];echo
"Odd :\n";
print_r(array_filter($array1, "odd"));
echo "Even:\n";
print_r(array_filter($array2, "even"));
?>
The above example will output:
Odd :
Array
(
[a] => 1
[c] => 3
[e] => 5
)
Even:
Array
(
[0] => 6
[2] => 8
[4] => 10
[6] => 12
)
Example #2 array_filter() without callback
<?php
$entry
= [
0 => 'foo',
1 => false,
2 => -1,
3 => null,
4 => '',
5 => '0',
6 => 0,
];print_r(array_filter($entry));
?>
The above example will output:
Array
(
[0] => foo
[2] => -1
)
Example #3 array_filter() with mode
<?php
$arr
= ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];var_dump(array_filter($arr, function($k) {
return $k == 'b';
}, ARRAY_FILTER_USE_KEY));var_dump(array_filter($arr, function($v, $k) {
return $k == 'b' || $v == 4;
}, ARRAY_FILTER_USE_BOTH));
?>
The above example will output:
array(1) {
["b"]=>
int(2)
}
array(2) {
["b"]=>
int(2)
["d"]=>
int(4)
}
Notes
Caution
If the array is changed from the callback function (e.g. element added, deleted or unset) the behavior of this function is undefined.
See Also
- array_intersect() - Computes the intersection of arrays
- array_map() - Applies the callback to the elements of the given arrays
- array_reduce() - Iteratively reduce the array to a single
value using a callback function
- array_walk() - Apply a user supplied function to every member of an array
Anonymous ¶
9 years ago
If you want a quick way to remove NULL, FALSE and Empty Strings (""), but leave values of 0 (zero), you can use the standard php function strlen as the callback function:
eg:
<?php// removes all NULL, FALSE and Empty Strings but leaves 0 (zero) values
$result = array_filter( $array, 'strlen' );?>
nicolaj dot knudsen at gmail dot com ¶
5 years ago
If you like me have some trouble understanding example #1 due to the bitwise operator (&) used, here is an explanation.
The part in question is this callback function:
<?php
function odd($var)
{
// returns whether the input integer is odd
return($var & 1);
}
?>
If given an integer this function returns the integer 1 if $var is odd and the integer 0 if $var is even.
The single ampersand, &, is the bitwise AND operator. The way it works is that it takes the binary representation of the two arguments and compare them bit for bit using AND. If $var = 45, then since 45 in binary is 101101 the operation looks like this:
45 in binary: 101101
1 in binary: 000001
------
result: 000001
Only if the last bit in the binary representation of $var is changed to zero (meaning that the value is even) will the result change to 000000, which is the representation of zero.
ASchmidt at Anamera dot net ¶
1 year ago
Depending on the intended meanings of your "empty" array values, e.g., null and empty string, vs. an integer 0 or a boolean false, be mindful of the result of different filters.
<?php
declare(strict_types=1);$array = array( 'null' => null, 'nullstring' => '', 'intzero' => 0, 'stringzero' => '0', 'false' => false, 'stringfalse' => 'false', );// Removes null, null-string -- but also FALSE!
$filtered1 = array_filter( $array, 'strlen' );// Removes only null.
$filtered2 = array_filter( $array, function( $v ) { return !is_null( $v ); } );// Removes null and null-string. Keeps FALSE and 0.
$filtered3 = array_filter( $array, function( $v ) { return !( is_null( $v) or '' === $v ); } );var_dump( $array, $filtered1, $filtered2, $filtered3 );
?>
Results in:
array (size=3)
'intzero' => int 0
'stringzero' => string '0' (length=1)
'stringfalse' => string 'false' (length=5)
array (size=5)
'nullstring' => string '' (length=0)
'intzero' => int 0
'stringzero' => string '0' (length=1)
'false' => boolean false
'stringfalse' => string 'false' (length=5)
array (size=4)
'intzero' => int 0
'stringzero' => string '0' (length=1)
'false' => boolean false
'stringfalse' => string 'false' (length=5)
TechNyquist ¶
4 months ago
Keep in mind that, as of PHP 7.4 and above, you can use arrow functions to as argument.
So for example if you want to leave values bigger than 10:
<?php
$arr = array_filter($numbers, fn($n) => $n > 10);
?>
also, combine with key-flag to cut certain keys:
<?php
$arr = array_filter($entries, fn($key) => !in_array($key, ['key1', 'key5']), ARRAY_FILTER_USE_KEY);
?>
and so on.
marc dot vanwoerkom at fernuni-hagen dot de ¶
18 years ago
Some of PHP's array functions play a prominent role in so called functional programming languages, where they show up under a slightly different name:
<?php
array_filter() -> filter(),
array_map() -> map(),
array_reduce() -> foldl() ("fold left")
?>
Functional programming is a paradigm which centers around the side-effect free evaluation of functions. A program execution is a call of a function, which in turn might be defined by many other functions. One idea is to use functions to create special purpose functions from other functions.
The array functions mentioned above allow you compose new functions on arrays.
E.g. array_sum = array_map("sum", $arr).
This leads to a style of programming that looks much like algebra, e.g. the Bird/Meertens formalism.
E.g. a mathematician might state
map(f o g) = map(f) o map(g)
the so called "loop fusion" law.
Many functions on arrays can be created by the use of the foldr() function (which works like foldl, but eating up array elements from the right).
I can't get into detail here, I just wanted to provide a hint about where this stuff also shows up and the theory behind it.
marc dot gray
at gmail dot com ¶
8 years ago
My favourite use of this function is converting a string to an array, trimming each line and removing empty lines:
<?php
$array = array_filter(array_map('trim', explode("\n", $string)), 'strlen');
?>
Although it states clearly that array keys are preserved, it's important to note this includes numerically indexed arrays. You can't use a for loop on $array above without processing it through array_values() first.
Niko E ¶
4 days ago
Note that a filtered array no longer encodes to json arrays, as the indices are no longer continuous:
$a = ['a', 'b', 'c'];
var_dump(json_encode($a)); // ["a","b","c"]
$a = array_filter($a, function ($x) { return $x == 'b'; });
var_dump(json_encode($a)); // {"1": "b"}
you can use array_values get a continuous array
var_dump(json_encode(array_values($a))); // ["b"]
justinphiggs at gmail dot com ¶
2 months ago
Check if all elements in array are not empty/null/falsy.
------------------------------
Supposing you have a one dimensional array...
<?php
$spicy_numbers = [69, 420, ɸ];
?>
And you want to easily check that all elements in said array are not null/empty/any falsy value, instead of running a loop over each element, you can pass the array to <?php array_filter() ?>, with no callback function, and then check if the returned array is the same size as the original, since <?php array_filter() ?> strips out all non-truthy values including 0 when no callback is provided.
Example:
<?php
$spicy_numbers = [69, 420, '']; // Phi is gone!if ( count( array_filter( $spicy_numbers ) ) !== count( $spicy_numbers ) ) {
// One of the elements is empty/null/falsy.
} else {
// All elements present and truthy.
}
?>
As a neat little function, you could do this:
<?php
/**
* Checks if all of given array's elements have a non-falsy value.
* Use-case: If all items in array are set and have a value (truthy, of course), then do X; else, do Y.
*
* @param array $arr
* @return bool
*/
function is_array_full( $arr ) {
$array_count = count( $arr );
$filtered_count = count( array_filter( $arr ) );
return (
$array_count === $filtered_count ) ? true : false;
}
?>
What is -> in PHP? This is referred to as the
object operator, or sometimes the single arrow operator. It is an access operator used for access/call methods and properties in a PHP object in Object-Oriented Programming (OOP).
