(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)
array_filter — Filters elements of an array using a callback function
DescriptionArray keys are preserved, and may result in gaps if the array was indexed. The result array can be reindexed using the array_values() function.
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 valueARRAY_FILTER_USE_BOTH - pass both value and key as arguments to callback instead of the value0 which will pass value as the only argument to callback instead.
Returns the filtered array.
Changelog Version Description 8.0.0callback 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' || $v == 4;
}, ARRAY_FILTER_USE_BOTH));
?>
The above example will output:
array(1) {
["b"]=>
int(2)
}
array(2) {
["b"]=>
int(2)
["d"]=>
int(4)
} Notes Caution
If the array is changed from the callback function (e.g. element added or unset) the behavior of this function is undefined.
See Also12 years ago
If you want a quick way to remove NULL, FALSE and Empty Strings (""), but leave values of 0 (zero), you can use the standard php function strlen as the callback function:
eg:
<?php$result = array_filter( $array, 'strlen' );?> Niko E ¶
2 years 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($a))); // ["b"]
Merlindog ¶
1 year ago
It is clearly documented above, but make sure you never forget that when ARRAY_FILTER_USE_BOTH is set, the callback argument order is value, key - NOT key, value. You'll save some time.
8 years ago
If you like me have some trouble understanding example #1 due to the bitwise operator (&) used, here is an explanation.
The part in question is this callback function:
<?php
function odd($var)
{
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.
TechNyquist ¶
2 years 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 ¶
20 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", $arr).
This leads to a style of programming that looks much like algebra, e.g. the Bird/Meertens formalism.
E.g. a mathematician might state
map(f o g) = map(f) o map(g)
the so called "loop fusion" law.
Many functions on arrays can be created by the use of the foldr() function (which works like foldl, but eating up array elements from the right).
I can't get into detail here, I just wanted to provide a hint about where this stuff also shows up and the theory behind it.
Hayley Watson ¶
1 year ago
The fact that array_filter preserves keys makes partitioning an array into [elements that pass the test, elements that fail the test] quite easy. In essence:
<?php
function partition($array, $test)
{
$pass = array_filter($array, $test);
$fail = array_diff_key($array, $pass);
return [false => $fail, true => $pass];
}
?>
The array_diff_key call is key; indexing the returned array as shown allows lines like "$failures = $partition[false];" to do the right thing (the booleans get converted to integers of course, but it's consistent and self-documenting). ASchmidt at Anamera dot net ¶
3 years ago
Depending on the intended meanings of your "empty" array values, e.g., null and empty string, vs. an integer 0 or a boolean false, be mindful of the result of different filters.
<?php
declare(strict_types=1);$array = array( 'null' => null, 'nullstring' => '', 'intzero' => 0, 'stringzero' => '0', 'false' => false, 'stringfalse' => 'false', );$filtered1 = array_filter( $array, 'strlen' );$filtered2 = array_filter( $array, function( $v ) { return !is_null( $v ); } );$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) marc dot gray at gmail dot com ¶
11 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 $array above without processing it through array_values() first. mail at sjappa dot nl ¶
16 days ago
Please note that the examples above will result into error "E_DEPRECATED: strlen(): Passing null to parameter #1 ($string) of type string is deprecated" on PHP 8.1.0 and above.
<?php
declare(strict_types=1);$array = array( 'null' => null, 'nullstring' => '', 'intzero' => 0, 'stringzero' => '0', 'false' => false, 'stringfalse' => 'false', );$filtered1 = array_filter( $array, 'strlen' );?>
In order to use strlen on an array with null values, add/use strval, see the example below:
<?php
declare(strict_types=1);$array = array( 'null' => null, 'nullstring' => '', 'intzero' => 0, 'stringzero' => '0', 'false' => false, 'stringfalse' => 'false', );$filtered1 = array_filter( $array, function($v) { return strlen(strval($v)); } );?>
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