PHP 8.4.0 Alpha 2 available for testing

array_filter

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

array_filter Filtra gli elementi di un array usando una funzione callback

Descrizione

array_filter(array $input, callback $callback = ?): array

array_filter() esegue un'iterazione su ogni valore nell' array input passandolo alla funzione. Se funzione restituisce true, il valore corrente di input viene restituito nell'array risultato. Le chiavi sono mantenute.

Example #1 Esempio di array_filter()

<?php
function dispari($var)
{
return(
$var % 2 == 1);
}

function
pari($var)
{
return(
$var % 2 == 0);
}

$array1 = array("a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
$array2 = array(6, 7, 8, 9, 10, 11, 12);

echo
"Dispari :\n";
print_r(array_filter($array1, "dispari");
echo
"Pari :\n";
print_r(array_filter($array2, "pari");
?>

Il precedente esempio visualizzerà:

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

Gli utenti non possono modificare l'array attraverso la funzione di callback, ad esempio aggiungere/togliere un elemento, o cancellare l'array su cui array_filter() è applicata. Se l'array viene cambiato, il comportamento di questa funzione non è definito.

Se la funzione callback non viene indicata, array_filter() rimuoverà tutti gli elementi di input che siano uguali a false. Vedere conversione a boolean per ulteriori informazioni.

Example #2 array_filter() senza callback

<?php

$entry
= array(
0 => 'pippo',
1 => false,
2 => -1,
3 => null,
4 => ''
);

print_r(array_filter($entry));
?>

Il precedente esempio visualizzerà:

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

Vedere anche array_map() e array_reduce().

add a note

User Contributed Notes 10 notes

up
622
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' );

?>
up
25
Niko E
1 year 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"]
up
9
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.
up
14
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.
up
47
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.
up
2
Hayley Watson
11 months 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).
up
36
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.
up
9
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.
up
2
ASchmidt at Anamera dot net
2 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)
up
-3
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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