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array_filter

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

array_filterFiltra elementos de um array utilizando uma função callback

Descrição

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

Itera sobre cada valor de array passando-os para a função callback. Se a função callback retornar true, o valor atual de array é retornado no array resultante.

Chaves do array são preservadas,e podem resultar em lacunas se o array foi indexado. O array resultante pode ser reindexado usando a função array_values().

Parâmetros

array

O array a ser iterado

callback

A função callback a ser usada

Se nenhum callback é fornecido, todas entradas vazias do array serão removidas. Veja empty() para saber como o PHP define vazia nesse caso.

mode

Flag determinando quais argumentos são passados para callback:

  • ARRAY_FILTER_USE_KEY - passa chaves como argumentos para callback em vez de valor
  • ARRAY_FILTER_USE_BOTH - passa tanto valor quanto chave como argumento para callback em vez do valor
Padrão é 0 que em vez disso irá passar valor como o único argumento para callback.

Valor Retornado

Retorna o array filtrado.

Registro de Alterações

Versão Descrição
8.0.0 callback agora é anulável.
8.0.0 Se a função callback espera que um parâmetro seja passado por referência, esta função agora emitirá um E_WARNING.

Exemplos

Exemplo #1 Exemplo da função array_filter()

<?php
function impar($var)
{
// retorna se o inteiro informado é impar
return $var & 1;
}

function
par($var)
{
// retorna se o inteiro informado é par
return !($var & 1);
}

$array1 = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5];
$array2 = [6, 7, 8, 9, 10, 11, 12];

echo
"Ímpares: \n";
print_r(array_filter($array1, "impar"));
echo
"Pares: \n";
print_r(array_filter($array2, "par"));
?>

O exemplo acima produzirá:

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

Exemplo #2 array_filter() sem callback

<?php

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

print_r(array_filter($entry));
?>

O exemplo acima produzirá:

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

Exemplo #3 array_filter() com 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));
?>

O exemplo acima produzirá:

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

Notas

Cuidado

Se o array é modificado por uma função callback (e.g. elemento adicionado, deletado ou apagado) o comportamento desta função é indefinido.

Veja Também

  • array_intersect() - Calcula a interseção entre arrays
  • array_map() - Aplica uma função em todos os elementos dos arrays dados
  • array_reduce() - Reduz um array para um único valor através de um processo iterativo via callback
  • array_walk() - Aplica uma determinada função em cada elemento de um array

add a note

User Contributed Notes 10 notes

up
612
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
22
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
4
Merlindog
7 months 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
1 year 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
44
nicolaj dot knudsen at gmail dot com
6 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
34
marc dot vanwoerkom at fernuni-hagen dot de
19 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
10
marc dot gray at gmail dot com
9 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
1
Hayley Watson
6 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
-2
justinphiggs at gmail dot com
1 year 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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