array_filter

(PHP 4 >= 4.0.6, PHP 5)

array_filterFilters elements of an array using a callback function

Description

array array_filter ( array $array = array() [, callable $callback = Function() ] )

Iterates over each value in the array passing them to the callback function. If the callback function returns true, the current value from array is returned into the result array. Array keys are preserved.

Parameters

array

The array to iterate over

callback

The callback function to use

If no callback is supplied, all entries of array equal to FALSE (see converting to boolean) will be removed.

Return Values

Returns the filtered array.

Examples

Example #1 array_filter() example

<?php
function odd($var)
{
    
// returns whether the input integer is odd
    
return($var 1);
}

function 
even($var)
{
    
// returns whether the input integer is even
    
return(!($var 1));
}

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

echo 
"Odd :\n";
print_r(array_filter($array1"odd"));
echo 
"Even:\n";
print_r(array_filter($array2"even"));
?>

The above example will output:

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

Example #2 array_filter() without callback

<?php

$entry 
= array(
             
=> 'foo',
             
=> false,
             
=> -1,
             
=> null,
             
=> ''
          
);

print_r(array_filter($entry));
?>

The above example will output:

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

Notes

Caution

If the array is changed from the callback function (e.g. element added, deleted or unset) the behavior of this function is undefined.

See Also

  • array_map() - Applies the callback to the elements of the given arrays
  • array_reduce() - Iteratively reduce the array to a single value using a callback function
  • array_walk() - Apply a user function to every member of an array

Коментарии

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.
2004-07-05 11:09:16
http://php5.kiev.ua/manual/ru/function.array-filter.html
Автор:
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' );

?>
2013-01-13 19:52:07
http://php5.kiev.ua/manual/ru/function.array-filter.html
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.
2014-04-29 13:44:43
http://php5.kiev.ua/manual/ru/function.array-filter.html
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.
2017-04-05 15:05:22
http://php5.kiev.ua/manual/ru/function.array-filter.html
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)
2021-09-08 20:24:42
http://php5.kiev.ua/manual/ru/function.array-filter.html
Автор:
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.
2022-05-13 21:36:17
http://php5.kiev.ua/manual/ru/function.array-filter.html
Check if all elements in array are not empty/null/falsy.
------------------------------
Supposing you have a one dimensional array...

<?php
  $spicy_numbers 
= [69420ɸ];
?>

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 
= [69420'']; // Phi is gone!

 
if ( countarray_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 );
   
$filtered_count countarray_filter$arr ) );
   
    return ( 
$array_count === $filtered_count ) ? true false;
  }
?>
2022-07-03 23:51:15
http://php5.kiev.ua/manual/ru/function.array-filter.html
Автор:
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"]
2022-09-14 18:24:05
http://php5.kiev.ua/manual/ru/function.array-filter.html
Автор:
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.
2023-06-27 17:43:54
http://php5.kiev.ua/manual/ru/function.array-filter.html
Автор:
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 => $failtrue => $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).
2023-07-25 09:20:39
http://php5.kiev.ua/manual/ru/function.array-filter.html

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