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array_filter

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

array_filterFiltra elementos de un array usando una función de devolución de llamada

Descripción

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

Recorre cada valor de array, pasándolos a la función callback. Si la función callback devuelve true el valor actual desde array es devuelto al array resultante. Las claves del array se conservan.

Parámetros

array

El array a recorrer.

callback

La función de devolución de llamada a usar.

Si no se proporciona callback, todas las entradas de array iguales a false (véase convetir a boolean) serán eliminadas.

flag

Indicador que determina qué argumentos se envían a callback:

  • ARRAY_FILTER_USE_KEY - pasar la clave como el único argumento a callback en lugar del valor
  • ARRAY_FILTER_USE_BOTH - pasar el valor y la clave como argumentos a callback en lugar del valor
Por omisión es 0 que pasará el valor como el único argumento a callback en su lugar.

Valores devueltos

Devuelve el array filtrado.

Historial de cambios

Versión Descripción
5.6.0 Se añadió el parámetro opcional flag y las constantes ARRAY_FILTER_USE_KEY y ARRAY_FILTER_USE_BOTH

Ejemplos

Ejemplo #1 Ejemplo de array_filter()

<?php
function impar($var)
{
    
// Retorna siempre que el número entero sea impar
    
return $var 1;
}

function 
par($var)
{
    
// Retorna siempre que el número entero sea par
    
return !($var 1);
}

$array1 = ['a' => 1'b' => 2'c' => 3'd' => 4'e' => 5];
$array2 = [6789101112];

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

El resultado del ejemplo sería:

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

Ejemplo #2 array_filter() sin callback

<?php

$entrada 
= [
    
=> 'foo',
    
=> false,
    
=> -1,
    
=> null,
    
=> '',
    
=> '0',
    
=> 0,
];

print_r(array_filter($entrada));
?>

El resultado del ejemplo sería:

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

Ejemplo #3 array_filter() con 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));
?>

El resultado del ejemplo sería:

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

Notas

Precaución

Si el array se cambia desde la función de devolución de llamada (p.ej. un elemento añadido, suprimido o desestablecido) el comportamiento de esta función no estará definido.

Ver también

  • array_map() - Aplica la retrollamada a los elementos de los arrays dados
  • array_reduce() - Reduce iterativamente un array a un solo valor usando una función llamada de retorno
  • array_walk() - Aplicar una función proporcionada por el usuario a cada miembro de un array

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User Contributed Notes 5 notes

up
530
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
29
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
9
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.
up
0
ASchmidt at Anamera dot net
1 month 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)
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