array_filter()

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

用回调函数过滤数组中的单元

说明

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

依次将$array数组中的每个值传递到$callback函数。如果$callback函数返回 true，则$array数组的当前值会被包含在返回的结果数组中。数组的键名保留不变。

参数

$array

要循环的数组

$callback

使用的回调函数

如果没有提供$callback函数，将删除$array中所有等值为FALSE的条目。更多信息见转换为布尔值。

$flag

决定$callback接收的参数形式:

• ARRAY_FILTER_USE_KEY-$callback接受键名作为的唯一参数
• ARRAY_FILTER_USE_BOTH-$callback同时接受键名和键值

返回值

返回过滤后的数组。

更新日志

范例

Example #1array_filter()例子

<?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);
$array2 = array(6, 7, 8, 9, 10, 11, 12);
echo "Odd :\n";
print_r(array_filter($array1, "odd"));
echo "Even:\n";
print_r(array_filter($array2, "even"));
?>

以上例程会输出：

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

不使用$callback时的array_filter()

<?php
$entry = array(
             0 => 'foo',
             1 => false,
             2 => -1,
             3 => null,
             4 => ''
          );
print_r(array_filter($entry));
?>

以上例程会输出：

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

带$flag标记的array_filter()

<?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));
?>

以上例程会输出：

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

注释

用户不应在回调函数中修改数组本身。例如增加／删除单元或者对array_filter()正在作用的数组进行 unset。如果数组改变了，此函数的行为将不可预测。

参见

• array_map() 为数组的每个元素应用回调函数
• array_reduce() 用回调函数迭代地将数组简化为单一的值
• array_walk() 使用用户自定义函数对数组中的每个元素做回调处理

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' );
?>

Because array_filter() preserves keys, you should consider the resulting array to be an associative array even if the original array had integer keys for there may be holes in your sequence of keys. This means that, for example, json_encode() will convert your result array into an object instead of an array. Call array_values() on the result array to guarantee json_encode() gives you an array.

In case you are interested (like me) in filtering out elements with certain key-names, array_filter won't help you. Instead you can use the following:
<?php
$arr = array( 'element1' => 1, 'element2' => 2, 'element3' => 3, 'element4' => 4 );
$filterOutKeys = array( 'element1', 'element4' );
$filteredArr = array_diff_key( $arr, array_flip( $filterOutKeys ) )
?>
Result will be something like this:
['element2'] => 2
['element3'] => 3

Here is how you could easily delete a specific value from an array with array_filter:
<?php
$array = array (1, 3, 3, 5, 6);
$my_value = 3;
$filtered_array = array_filter($array, function ($element) use ($my_value) { return ($element != $my_value); } );
print_r($filtered_array);
?>
output:
Array
(
  [0] => 1
  [3] => 5
  [4] => 6
)

array_filter remove also FALSE and 0. To remove only NULL's use:
$af = [1, 0, 2, null, 3, 6, 7];
function is_not_null($val){
  return !is_null($val);
}
$af = array_filter($af, 'is_not_null');

If you want to use array_filter with a class method as the callback, you can use a psuedo type callback like this:
<?php
class Test
{
  public function doFilter($array)
  {
    return array_filter($array, array($this, 'callbackMethodName'));
  }
  protected function callbackMethodName($element)
  {
    return $element % 2 === 0;
  }
}
$example = new Test;
print_r($example->doFilter(range(1, 10)));
?>
Will return even numbers.

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.

Here's a function that will filter a multi-demensional array. This filter will return only those items that match the $value given
<?php
  /*
   * filtering an array
   */
  function filter_by_value ($array, $index, $value){ 
    if(is_array($array) && count($array)>0) 
    { 
      foreach(array_keys($array) as $key){
        $temp[$key] = $array[$key][$index];
         
        if ($temp[$key] == $value){
          $newarray[$key] = $array[$key];
        }
      }
     }
   return $newarray; 
  } 
?>
Example:
<?php
$results = array(
  0 => array('key1' => '1', 'key2' => 2, 'key3' => 3),
  1 => array('key1' => '12', 'key2' => 22, 'key3' => 32) 
);
$nResults = filter_by_value($results, 'key2', '2');
?>
Output :
array(
  0 => array('key1' => '1', 'key2' => 2, 'key3' => 3)
);

This function filters an array and remove all null values recursively.
<?php
 function array_filter_recursive($input)
 {
  foreach ($input as &$value)
  {
   if (is_array($value))
   {
    $value = array_filter_recursive($value);
   }
  }
  
  return array_filter($input);
 }
?>
Or with callback parameter (not tested) :
<?php
 function array_filter_recursive($input, $callback = null)
 {
  foreach ($input as &$value)
  {
   if (is_array($value))
   {
    $value = array_filter_recursive($value, $callback);
   }
  }
  
  return array_filter($input, $callback);
 }
?>

<?php
function array_filter_recursive ($data) {
  $original = $data;
  $data = array_filter($data);
  
  $data = array_map(function ($e) {
    return is_array($e) ? array_filter_recursive($e) : $e;
  }, $data);
  return $original === $data ? $data : array_filter_recursive($data);
}
$data = ['a' => 0, 'b' => [], 'c' => [[]], 'd' => [[[[]]]], 'e' => 'foo', 'f' => [[['a']]], [true], [[],['a'], [true, false]]];
$data = array_filter_recursive($data);
?>

You can access the current key of array by passing a reference to array into callback function and call key() and next() method in the callback function:
<?php
$data = array('first' => 1, 'second' => 2, 'third' => 3);
$data = array_filter($data, function ($item) use (&$data) {
  echo "Filtering key ", key($data), '<br>', PHP_EOL;
  next($data);
  return false;
});
?>
However be careful with array internal pointer or use reset() method before calling array_filter().

from php 5.3, we use anonymous function as second argument:
$a = array('a'=>1, 'b'=>2, 'c'=>false, 'd'=>0);
$b = array_filter($a, function($v){return $v !== 0;});
var_dump($b);
output:
array(3) {
 'a' =>
 int(1)
 'b' =>
 int(2)
 'c' =>
 bool(false)
}

To get rid of all white space in an array without looping.
<?php
  $array = array(5, "  ", 2, NULL, 13, "", 7, "\n", 4, "\t");
  print_r($array);
  $result = array_filter($array, create_function('$a','return preg_match("#\S#", $a);'));         
  print_r($result);
?>
Array
(
  [0] => 5
  [1] =>  
  [2] => 2
  [3] => 
  [4] => 13
  [5] => 
  [6] => 7
  [7] => 
  [8] => 4
  [9] =>   
)
Array
(
  [0] => 5
  [2] => 2
  [4] => 13
  [6] => 7
  [8] => 4
)

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.

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.

This function trims empty strings from the beginning and end of an array.
It's useful when outputing plaintext files on a page and you want to skip empty lines at the beginning and end, but not within the text.
<?php
function array_trim($array) {
  while (strlen(reset($array)) === 0) {
    array_shift($array);
  }
  while (strlen(end($array)) === 0) {
    array_pop($array);
  }
  return $array;
}
?>
You might want to trim each element too.

If you want to pass the key to the callback function before PHP 5.6.0 (when the flag parameter wasn't implemented):
<?php
$result = array_filter(array_keys($array), 'is_int');
?>

You can use array_filter from within a class to access a protected method from that same class:
<?php
class Bar {
  public function foo()
  {
    $array1 = array("a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
    print_r(array_filter($array1, array($this, 'naz')));
  }
  protected function baz($var)
  {
    return($var & 1);
  }
}
$bar = new Bar();
$bar->foo();
?>

nice trick:
$array_out = array_filter($array_in, function($var) use($array_other) {
      return in_array($var, $array_other) ? true : false;
});

be careful with the above function "array_delete"'s use of the stristr function, it could be slightly misleading. consider the following:
<?php
function array_delete($array, $filterforsubstring){
  $thisarray = array ();
  foreach($array as $value)
    if(stristr($value, $filterforsubstring)===false && strlen($value)>0)
      $thisarray[] = $value;
  return $thisarray;
}
function array_delete2($array, $filterforstring, $removeblanksflag=0){
  $thisarray = array ();
  foreach($array as $value)
    if(!(stristr($value, $filterforstring) && strlen($value)==strlen($filterforstring))
        && !(strlen($value)==0 && $removeblanksflag))
      $thisarray[] = $value;
  return $thisarray;
}
function array_delete3($array, $filterfor, $substringflag=0, $removeblanksflag=0){
  $thisarray = array ();
  foreach($array as $value)
    if(
      !(stristr($value, $filterfor) 
        && ($substringflag || strlen($value)==strlen($filterfor))
      )
      && !(strlen($value)==0 && $removeblanksflag)
    )
      $thisarray[] = $value;
  return $thisarray;
}
$array1 = array ('the OtHeR thang','this', 'that', 'OtHer','', 9, 101, 'fifty', ' oTher', 'otHer ','','other','Other','','other blank things');
echo "<pre>array :\n";
print_r($array1);
$array2=array_delete($array1, "Other");
echo "array_delete(\$array1, \"Other\"):\n";
print_r($array2);
$array2=array_delete2($array1, "Other");
echo "array_delete2(\$array1, \"Other\"):\n";
print_r($array2);
$array2=array_delete2($array1, "Other",1);
echo "array_delete2(\$array1, \"Other\",1):\n";
print_r($array2);
$array2=array_delete3($array1, "Other",1);
echo "array_delete3(\$array1, \"Other\",1):\n";
print_r($array2);
$array2=array_delete3($array1, "Other",0,1);
echo "array_delete3(\$array1, \"Other\",0,1):\n";
print_r($array2);
 ?>

Here is a simple array_grep() function that works similarly to 'grep' command, ie. filters array elements that match a given regular expression.
It's a bit ugly as it uses a global variable $__array_grep_regex to pass the regular expression to the callback function. I couldn't find a better way to do it. Anyway, here it is:
<?php
$__array_grep_regex="";
function array_grep($arr, $regex) {
global $__array_grep_regex;
$__array_grep_regex=$regex;
return array_filter($arr, function($val) {
 global $__array_grep_regex;
 return preg_match($__array_grep_regex, $val);
});
}
?>

If we need to find array in the multidimenssional array (with ignore keys!)
// where we will find
$arrays = [
  ['c','b','a'], ['e','f','g'], ['j','h','t']
];
// what we will find  
$array = ['a','b','c'];
function isArrayExist($arrays, $array)
{
  return (bool) array_filter($arrays, function ($_array) use ($array) {
    return !array_diff($array, $_array);
  });
}
//Output
true

I needed to filter specific files. glob was a good option but had issues being case sensitive. And at the same time, I had to filter the directory names like ".", "..", ".git", etc which could be complex.
I used a snippet as below, where I could implement this complex filter. Just modify your method: image_file.
<?php
class handlers
{
  private $path;
  public function __construct($path)
  {
    $this->path = realpath($path);
  }
  public function image_file($file="abc.png")
  {
    $is_image_file = is_file($this->path."/".$file);
    return $is_image_file;
  }
}
$path = realpath("../../gallery-200x400");
$files = scandir($path);
print_r($files);
$files = array_filter($files, array(new handlers($path), "image_file"), ARRAY_FILTER_USE_BOTH);
print_r($files);
?>

Hi, when using your annonymous function to filter the array, DO NOT cast returning value as bool.
Any value won't be filtered that way.
example:
$reader = array(
  1,2,3,2,1,2,1,2,1
);
$a = array_filter($reader, function ($var) {
  return (bool) $var == 2;  //returns whole array
  return $var == 2;      //filter values
});
echo count($a);   //9 with cast as bool, 4 otherwise

If you have an array of KV pairs and you want all the items where a value is X, you dont need to make a callback for array_filter. You can use array_intersect:
<?php
print_r(array_intersect(
 array(
  'a' => 1,
  'b' => 1,
  'c' => 1,
  'd' => 2,
  'e' => 2,
  'f' => 2,
 ),
 array(1)
));
Array
(
  [a] => 1
  [b] => 1
  [c] => 1
)
?>
The advantage of this approach is you can pass variables into the second array without needing to worry about variable scope and function parameters for array_filter.

Here is key-passed array_filter function.
<?php
function arrayfilter(array $array, callable $callback = null) {
  if ($callback == null) {
    $callback = function($key, $val) {
      return (bool) $val;
    };
  }
  $return = array();
  foreach ($array as $key => $val) {
    if ($callback($key, $val)) {
      $return[$key] = $val;
    }
  }
  return $return;
}
$test_array = array('foo', 'a' => 'the a', 'b' => 'the b', 11 => 1101, '', null, false, 0);
$array = arrayfilter($test_array, function($key, $val) {
  return is_string($key);
});
print_r($array);
/*
Array
(
  [a] => the a
  [b] => the b
)
*/
$array = arrayfilter($test_array);
print_r($array);
/*
Array
(
  [0] => foo
  [a] => the a
  [b] => the b
  [11] => 1101
)
*/
?>

A function that allows filtering an array by keys:
<?php
function array_filter_key( $input, $callback ) {
  if ( !is_array( $input ) ) {
    trigger_error( 'array_filter_key() expects parameter 1 to be array, ' . gettype( $input ) . ' given', E_USER_WARNING );
    return null;
  }
  
  if ( empty( $input ) ) {
    return $input;
  }
  
  $filteredKeys = array_filter( array_keys( $input ), $callback );
  if ( empty( $filteredKeys ) ) {
    return array();
  }
  
  $input = array_intersect_key( array_flip( $filteredKeys ), $input );
  
  return $input;
}
?>
Example:
<?php
$input = array_flip( range( 'a', 'z' ) );
$consonants = array_filter_key( $arr, function( $elem ) {
  $vowels = "aeiou";
  return strpos( $vowels, strtolower( $elem ) ) === false;
} );
?>
Outputs:
array(21) {
 ["b"]=>
 int(1)
 ["c"]=>
 int(2)
 ["d"]=>
 int(3)
 ["f"]=>
 int(5)
 ["g"]=>
 int(6)
 ["h"]=>
 int(7)
 ["j"]=>
 int(9)
 ["k"]=>
 int(10)
 ["l"]=>
 int(11)
 ["m"]=>
 int(12)
 ["n"]=>
 int(13)
 ["p"]=>
 int(15)
 ["q"]=>
 int(16)
 ["r"]=>
 int(17)
 ["s"]=>
 int(18)
 ["t"]=>
 int(19)
 ["v"]=>
 int(21)
 ["w"]=>
 int(22)
 ["x"]=>
 int(23)
 ["y"]=>
 int(24)
 ["z"]=>
 int(25)
}

I use the following to see if a array consist of scalar values or null, but of course you could mix it up using any of the is_ functions.
<?php
if(count($data) !== count(array_filter($data, 'is_scalar') + array_filter($data, 'is_null'))) {
 throw new Exception('Array did not consist of scalar and null values');
}
?>

Regarding comment about trimming empty strings, the code posted will get into an infinite loop if the array is reduced to zero elements. The following might be better:
<?php
function array_trim($array) {
  while (!empty($array) and strlen(reset($array)) === 0) {
    array_shift($array);
  }
  while (!empty($array) and strlen(end($array)) === 0) {
    array_pop($array);
  }
  return $array;
}
?>

For any type of array. Basead in redshift code.
<?php
function array_clean ($array, $todelete = false, $caseSensitive = false) {
  foreach($array as $key => $value) {
    if(is_array($value)) {
      $array[$key] = array_clean($array[$key], $todelete, $caseSensitive);
    }
    else {
      if($todelete) {
        if($caseSensitive) {
          if(strstr($value ,$todelete) !== false)
            unset($array[$key]);
        }
        else {
          if(stristr($value, $todelete) !== false)
            unset($array[$key]);
        }
      }
      elseif (empty($value)) {
        unset($array[$key]);
      }
    }
  }
  return $array;
}
?>

I was looking for a function to delete values from an array and thought I had found it in array_filter(), however, I *didn't* want the keys to be preserved *and* I needed blank values cleaned out of the array as well. I came up with the following (with help from many of the above examples):
<?php
function array_delete($array, $filterfor){
 $thisarray = array ();
 foreach($array as $value)
  if(stristr($value, $filterfor)===false && strlen($value)>0)
   $thisarray[] = $value;
 return $thisarray;
}
$array1 = array ('OtHeR','this', 'that', 'Other','', 9, 101, 'fifty', 'other','','');
echo "<pre>array :\n";
print_r($array1);
$array2=array_delete($array1, "Other");
echo "filtered:\n";
print_r($array2);
?>

The following function modifies the supplied array recursively so that filtering is performed on multidimentional arrays as well, while preserving keys.
<?php
function array_cleanse(&$arr){
$temp = array();
reset($arr);
if(count($arr) == 0) return "";
foreach($arr as $key=>$val):
 (is_array($val))? array_cleanse($val) : NULL;
 ($val)? $temp[$key] = $val : NULL;
endforeach;
$arr = $temp;
reset($arr);
}
?>
$arr1 = array('a'=>20,'b'=>array(''),'c'=>array(1,0,2),'d'=>0);
array_cleanse($arr1);
$arr1 will be array('a'=>20,'c'=>array(1,2))
array_filter may not be used as it does not modify the array within itself.

<?php
// ARRAY FILTER RECURSIVE USING CLASS, STATIC METHOD, AND ANONYMOUS CALLBACK FUNCTION
// NOTE THAT THE CALLBACK HAS ACCESS TO BOTH THE KEY AND VALUE
// THE CLASS (FOR YOU TO COPY)
class ArrayUtil
{
  public static function FilterRecursive(Array $source, $fn)
  {
    $result = array();
    foreach ($source as $key => $value)
    {
      if (is_array($value))
      {
        $result[$key] = self::FilterRecursive($value, $fn);
        continue;
      }
      if ($fn($key, $value))
      {
        $result[$key] = $value; // KEEP
        continue;
      }
    }
    return $result;
  }
}
// EXAMPLE ANONYMOUS CALLBACK FUNCTION
$fn = function ($key, $value)
{
  if (strpos($key, 'drop') !== FALSE)
  {
    return FALSE; // DROP
  }
  return TRUE; // KEEP
};
// EXAMPLE PRE FILTER TEST DATA
$preFilter = array(
  'a' => 'one',
  'b' => array(
    'example_drop' => 'filter me out',
    'example_keep' => 'keep me',
  ),
  'c' => 'three',
);
// EXAMPLE USAGE CODE
echo '// print_r($preFilter);' . "\n";
print_r($preFilter);
$postFilter = ArrayUtil::FilterRecursive($preFilter, $fn);
echo "\n";
echo '// print_r($postFilter);' . "\n";
print_r($postFilter);
/* OUTPUT OPEN
// print_r($preFilter);
Array
(
  [a] => one
  [b] => Array
    (
      [example_drop] => filter me out
      [example_keep] => keep me
    )
  [c] => three
)
// print_r($postFilter);
Array
(
  [a] => one
  [b] => Array
    (
      [example_keep] => keep me
    )
  [c] => three
)
OUTPUT CLOSE */

Read "callback" parameter note with understanding (as well as "converting to boolean" chapter). Keep in midn, that 0, both:
* integer: 0 and
* float: 0.00
evaluates to boolean FALSE! And therefore all array nodes, that have such value WILL ALSO BE FILTERED by array_filter(), with default call back. Unless you provide your own callback function, that will (for example) filter only empty strings and NULLs, but leave "zeros" untouched.
Some people (including me) might be surprised to find this out.

If you have not noticed already - array_filter() can be used to remove empty elements, since an empty string considered "false", if you not specify a callback
Keep in mind, that this will remove also some other values - so if you want a quick "remove empty elements from array" this function will be fine, as long as you dont have anything to keep, which casts to "false"

<?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);
$array2 = array(6, 7, 8, 9, 10, 11, 12);
echo "Odd :\n";
print_r(array_filter($array1, "odd"));
echo "Even:\n";
print_r(array_filter($array2, "even"));
?>
shouldtnt the '&' operators in the function be a '%' ? Is this a typo or do I not undertsand PHP

If you want a quick way to Find Numbers ( remove NULL, FALSE and Empty Strings (""), all Strings) but leave values of 0 (zero)
eg:
<?php
/*
 Find Numbers (removes all NULL, FALSE and Empty Strings, all Strings) but leaves 0 (zero) values
*/
$result = array_filter( array( "0",0,1,2,3,'text' ) , 'is_numeric' );
var_dump($result);
/*
 array (size=5)
 0 => string '0' (length=1)
 1 => int 0
 2 => int 1
 3 => int 2
 4 => int 3
*/
?>