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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 = ?, int $flag = 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 na matriz resultado. As chaves do array são preservadas.

Parâmetros

array

O array a ser iterado

callback

A função callback a ser usada

Se nenhum callback é fornecido, todas entradas de array iguais a false (veja convertendo para booleano) serão removidas.

flag

Flag determina quais argumentos são passados para o parâmetro 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

Valor Retornado

Retorna o array filtrado.

Changelog

Versão Descrição
5.6.0 Adicionado o parâmetro opcional flag e as contantes ARRAY_FILTER_USE_KEY e ARRAY_FILTER_USE_BOTH

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

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

O exemplo acima irá imprimir:

Impares:
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 
= array(
             
=> 'foo',
             
=> false,
             
=> -1,
             
=> null,
             
=> ''
          
);

print_r(array_filter($entry));
?>

O exemplo acima irá imprimir:

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

Exemplo #3 array_filter() com flag

<?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 irá imprimir:

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_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 função callback
  • array_walk() - Aplica uma determinada funcão em cada elemento de um array

add a note add a note

User Contributed Notes 4 notes

up
527
Anonymous
8 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
4 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
17 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
8
marc dot gray at gmail dot com
7 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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