array_filter

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

array_filter — Filtert 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 = [6, 7, 8, 9, 10, 11, 12];

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 = [
    0 => 'foo',
    1 => false,
    2 => -1,
    3 => null,
    4 => '',
    5 => '0',
    6 => 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

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User Contributed Notes 10 notes

down

613

Anonymous ¶

11 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' );

?>

down

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"]

down

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.

down

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.

down

nicolaj dot knudsen at gmail dot com ¶

7 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.

down

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.

down

marc dot gray at gmail dot com ¶

10 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.

down

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', );

// 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)

down

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).

down

-2

justinphiggs at gmail dot com ¶

2 years 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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