Php array filter by value

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

array_filter — Filters elements of an array using a callback function

Description

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

Array keys are preserved, and may result in gaps if the array was indexed. The result array can be reindexed using the array_values() function.

Parameters

The array to iterate over

The callback function to use

If no callback is supplied, all empty entries of array will be removed. See empty() for how PHP defines empty in this case.

Flag determining what arguments are sent to callback:

• ARRAY_FILTER_USE_KEY - pass key as the only argument to callback instead of the value
• ARRAY_FILTER_USE_BOTH - pass both value and key as arguments to callback instead of the value

Return Values

Returns the filtered array.

Changelog

Examples

Example #1 array_filter() example

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

function

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

$entry

The above example will output:

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

Example #3 array_filter() with mode

$arr

The above example will output:

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

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_intersect() - Computes the intersection of arrays
• 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 supplied function to every member of an array

Anonymous ¶

9 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:
// removes all NULL, FALSE and Empty Strings but leaves 0 (zero) values
$result = array_filter( $array, 'strlen' );?>

nicolaj dot knudsen at gmail dot com ¶

5 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:

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.

ASchmidt at Anamera dot net ¶

1 year 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.

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)

TechNyquist ¶

4 months 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:

    $arr = array_filter($numbers, fn($n) => $n > 10);
?>

also, combine with key-flag to cut certain keys:

    $arr = array_filter($entries, fn($key) => !in_array($key, ['key1', 'key5']), ARRAY_FILTER_USE_KEY);
?>

and so on.

marc dot vanwoerkom at fernuni-hagen dot de ¶

18 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:

  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.

marc dot gray at gmail dot com ¶

8 years ago

My favourite use of this function is converting a string to an array, trimming each line and removing empty lines:

$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.

Niko E ¶

12 days 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"]

justinphiggs at gmail dot com ¶

2 months ago

Check if all elements in array are not empty/null/falsy.
------------------------------
Supposing you have a one dimensional array...

  $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 () ?>, with no callback function, and then check if the returned array is the same size as the original, since () ?> strips out all non-truthy values including 0 when no callback is provided.

Example:
  $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:
  /**
   * 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 (