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 == 1);
}

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

$array1 = array("a"=>1"b"=>2"c"=>3"d"=>4"e"=>5);
$array2 = array(6789101112);

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(
             
=> 'pippo',
             
=> false,
             
=> -1,
             
=> null,
             
=> ''
          
);

print_r(array_filter($entry));
?>

Il precedente esempio visualizzerà:

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

Vedere anche array_map() e array_reduce().

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User Contributed Notes 4 notes

up
528
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
17
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
28
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
9
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.
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