(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)
array_filter — Filtra elementos de un array usando una función de devolución de llamada
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.
arrayEl array a recorrer.
callbackLa 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
0 que pasará el valor como el único argumento
a callback en su lugar.
Devuelve el array filtrado.
| Versión | Descripción |
|---|---|
| 5.6.0 |
Se añadió el parámetro opcional flag y las constantes
ARRAY_FILTER_USE_KEY y
ARRAY_FILTER_USE_BOTH
|
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];
$array2 = [6, 7, 8, 9, 10, 11, 12];
echo "Impar :\n";
print_r(array_filter($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
$entrada = [
0 => 'foo',
1 => false,
2 => -1,
3 => null,
4 => '',
5 => '0',
6 => 0,
];
print_r(array_filter($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)
}
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.
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' );
?>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.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($a))); // ["b"]If you like me have some trouble understanding example #1 due to the bitwise operator (&) used, here is an explanation.
The part in question is this callback function:
<?php
function odd($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.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.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).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.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.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)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;
}
?>