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array_filter

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

array_filterFiltert Elemente eines Arrays mittels einer Callback-Funktion

Beschreibung

array_filter(array $array, ?callable $callback = null, int $mode = 0): array

Iteriert über jeden Wert im Array array und übergibt diesen der Callbackfunktion callback. Gibt die Funktion callback true zurück, so wird der aktuelle Wert von array in das Ergebnis-Array geschrieben.

Die Schlüssel bleiben erhalten, was zu Lücken führen kann, wenn array indexiert war. Das resultierende Array kann unter Verwendung der Funktion array_values() reindexiert werden.

Parameter-Liste

array

Das Array, über das iteriert werden soll

callback

Die zu verwendende Callbackfunktion

Falls die Funktion callback nicht angegeben wurde, werden alle leeren Einträge aus array entfernt. Siehe empty() zu Informationen was leer in diesem Fall bedeutet.

mode

Flag, welches bestimmt welche Parameter an callback gesendet werden:

  • ARRAY_FILTER_USE_KEY - statt des Wertes wird der Schlüssel als einziger Parameter an callback gesendet.
  • ARRAY_FILTER_USE_BOTH - statt nur des Wertes werden sowohl der Schlüssel als auch der Wert als Parameter an callback übergeben.
Der Standardwert ist 0, was bedeutet, dass nur der Wert als Parameter an callback übergeben wird.

Rückgabewerte

Gibt das gefilterte Array zurück.

Changelog

Version Beschreibung
8.0.0 callback ist jetzt nullbar.
8.0.0 Wenn callback einen per Referenz übergebenen Parameter erwartet, gibt diese Funktion nun einen Fehler der Stufe E_WARNING aus.

Beispiele

Beispiel #1 array_filter()-Beispiel

<?php
function ungerade($var)
{
    
// Gibt zurück, ob der Eingabewert ungerade ist
    
return $var 1;
}

function 
gerade($var)
{
    
// Gibt zurück, ob der Eingabewert gerade ist
    
return !($var 1);
}

$array1 = ["a"=>1"b"=>2"c"=>3"d"=>4"e"=>5];
$array2 = [6789101112];

echo 
"Ungerade :\n";
print_r(array_filter($array1"ungerade"));
echo 
"Gerade:\n";
print_r(array_filter($array2"gerade"));
?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Ungerade :
Array
(
    [a] => 1
    [c] => 3
    [e] => 5
)
Gerade:
Array
(
    [0] => 6
    [2] => 8
    [4] => 10
    [6] => 12
)

Beispiel #2 array_filter() ohne callback

<?php

$entry 
= [
    
=> 'foo',
    
=> false,
    
=> -1,
    
=> null,
    
=> '',
    
=> '0',
    
=> 0,
];

print_r(array_filter($entry));
?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Array
(
    [0] => foo
    [2] => -1
)

Beispiel #3 array_filter() mit 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));
?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

array(1) {
  ["b"]=>
  int(2)
}
array(2) {
  ["b"]=>
  int(2)
  ["d"]=>
  int(4)
}

Anmerkungen

Achtung

Wird das Array durch die Callbackfunktion verändert (z. B. durch Hinzufügen, Löschen oder Zurücksetzen eines Elements), so ist das Verhalten dieser Funktion undefiniert.

Siehe auch

  • array_intersect() - Ermittelt die Schnittmenge von Arrays
  • array_map() - Wendet eine Callback-Funktion auf die Elemente von Arrays an
  • array_reduce() - Reduziert das Array mittels einer Callback-Funktion iterativ auf einen einzigen Wert
  • array_walk() - Wendet eine vom Benutzer gelieferte Funktion auf jedes Element eines Arrays an

add a note

User Contributed Notes 7 notes

up
568
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' );

?>
up
30
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.
up
4
ASchmidt at Anamera dot net
10 months 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)
up
30
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.
up
1
TechNyquist
2 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.
up
11
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.
up
0
justinphiggs at gmail dot com
1 month 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;
  }
?>
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