PHP TOP

array_find »

« array_fill_keys

array_filter

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

array_filter — コールバック関数を使用して、配列の要素をフィルタリングする

説明

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

callback 関数によりフィルタ処理が行われた array の全ての要素を含む配列を返します。 callback 関数が true を返した場合、 array の現在の値が結果の配列に入ります。

配列のキーは保存されます。 array にインデックスが振られていた場合、結果が異なる場合があります。結果の array のインデックスは、 array_values() 関数を使って振り直すことができます。

パラメータ

array

処理する配列。

callback

使用するコールバック関数。

コールバック関数が与えられなかった場合、 array のエントリの中で空のものはすべて削除されます。この場合の「空」の定義については、empty() 関数を参照ください。

mode

引数として、何を callback に送るのかを決めるフラグ。

ARRAY_FILTER_USE_KEY - 値ではなく、キーだけを callback の引数として渡す
ARRAY_FILTER_USE_BOTH - 値だけではなく、値とキーの両方を callback の引数として渡す

デフォルトは 0 で値のみをcallbackの引数として渡します。

戻り値

フィルタリングされた結果の配列を返します。

変更履歴

バージョン	説明
8.0.0	`callback` は、nullable になりました。
8.0.0	`callback` がリファレンス渡しされる引数を期待している場合、この関数は `E_WARNING` を発生させるようになりました。

例

例1 array_filter() の例

<?php
function odd($var)
{
    // 渡された整数が奇数かどうかを返します
    return $var & 1;
}

function even($var)
{
    // 渡された整数が偶数かどうかを返します
    return !($var & 1);
}

$array1 = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5];
$array2 = [6, 7, 8, 9, 10, 11, 12];

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

上の例の出力は以下となります。

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

例2 callback がない array_filter()

<?php

$entry = [
    0 => 'foo',
    1 => false,
    2 => -1,
    3 => null,
    4 => '',
    5 => '0',
    6 => 0,
];

print_r(array_filter($entry));
?>

上の例の出力は以下となります。

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

例3 array_filter() で mode を使う例

<?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));
?>

上の例の出力は以下となります。

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

注意

警告

配列の内容がコールバック関数内で変更された場合 (たとえば要素が追加されたりunsetされたりなど) のこの関数の挙動は未定義です。

参考

array_intersect() - 配列の共通項を計算する
array_find() - コールバック関数を満たす最初の要素を返す
array_any() - array のいずれかの要素がコールバック関数を満たすかどうかを調べる
array_map() - 指定した配列の要素にコールバック関数を適用する
array_reduce() - コールバック関数を繰り返し配列に適用し、配列をひとつの値にまとめる

Found A Problem?

Learn How To Improve This Page • Submit a Pull Request • Report a Bug

＋add a note

User Contributed Notes 10 notes

down

625

Anonymous ¶

11 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' );

?>

down

Merlindog ¶

1 year ago

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.

down

Niko E ¶

2 years 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"]

down

nicolaj dot knudsen at gmail dot com ¶

7 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.

down

TechNyquist ¶

2 years 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:

<?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.

down

Hayley Watson ¶

1 year ago

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).

down

marc dot vanwoerkom at fernuni-hagen dot de ¶

20 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.

down

marc dot gray at gmail dot com ¶

10 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.

down

ASchmidt at Anamera dot net ¶

3 years 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)

down

-3

justinphiggs at gmail dot com ¶

2 years ago

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;
  }
?>

＋add a note

Atelier ”慶”

WEBクリエイター歴２０年、最先端技術と安心をお届けします。

PHPのお勉強！

array_filter

説明

パラメータ

戻り値

変更履歴

例

注意

参考

Found A Problem?

User Contributed Notes 10 notes