php教程

array_filter

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

array_filter — 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

版本 说明
5.6.0 添加可选的参数 flag，以及常量 ARRAY_FILTER_USE_KEY 和 ARRAY_FILTER_USE_BOTH。

范例

Example #1 array_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
)

Example #2 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
)

Example #3 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

Caution

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

User Contributed Notes

raj at rafa dot eu dot org 17-Aug-2018 11:54
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);
});
}
?>
nsrwork(dog)gmail 01-Jun-2018 03:48
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
Anonymous 15-Mar-2018 09:10
<?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
bimal at sanjaal dot com 12-Dec-2017 11:29
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);
?>
jimmmy dot chief at gmail dot com 22-Sep-2017 03:50
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
nicolaj dot knudsen at gmail dot com 05-Apr-2017 12:05
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.
yuzhen huang 16-May-2015 01:49
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)
}
njt1982 at yahoo dot com 30-Apr-2015 01:18
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.
manuelworks at gmail dot com 16-Apr-2015 03:34
I needed to get the complete array element of a multilevel array where the values of some elements where 'x' or 'y'. Kind of a WHERE  AND in a MySQL Query..

SO if you need to filter an array where 'X' = Y and 'a' = b, here you go.

<?php
/*
 * getArrayElement() by @MmO12
 *
 * SELECT an element of  an $array...
 * *$array = array( 0 => array('index1'  => 'a', 'index2' => 'b', 'value' => 'hello'),
                1 => array('index1'  => 'a', 'index2' => 'c', 'value' => 'bye'));
*
 * WHERE its $indexs values  are equal to...
 * * $indexs = array('index1' => 'a', 'index2'=>'b');
 */
function getArrayElement($array, $indexs, $justvalsplease = false){
    $newarray = false;
    //verificamos el array
    if(is_array($array) && count($array)>0){
       
        //verify indexs and get # of indexs
        if(is_array($indexs) && count($indexs)>0) $ninds = count($indexs);
        else return false;
       
        //search for coincidences
        foreach(array_keys($array) as $key){

            //index value coincidence counter.
            $count = 0;
           
            //for each index we search           
            foreach($indexs as $indx => $val){
               
                //if index value is equal then counts
                if($array[$key][$indx] == $val){
                    $count++;
                }
            }
            //if indexes match, we get the array elements :)
            if($count == $ninds){
               
                //if you only need the vals of the first coincidence
                //witch was my case by the way...
                if($justvalsplease) return $array[$key];
                else $newarray[$key] = $array[$key];
            }
        }
    }
  return $newarray;
}
?>

/*******
Example
********/
<?php
   //array
    $array = array( 0 => array('index1'  => 'a', 'index2' => 'b', 'value' => 'hello'),
                  1 => array('index1'  => 'a', 'index2' => 'c', 'value' => 'bye'),
                  2 => array('index1'  => 'b', 'index2' => 'a', 'value' => 'hi'));

    //indexes
    $indexs = array('index1' => 'a', 'index2'=>'b');

    //aaand we get the element we want.
    $element = getArrayElement($array, $indexs);

        print_r($element);

    /***prints ***/
    Array
    (
        [0] => Array
            (
                [index1] => a
                [index2] => b
                [value] => hello
            )
   
    )?>

IF you want only the array inside the elements just set $justvalsplease true like this
<?php
     $element = getArrayElement($array, $indexs,true);
?>

And you will get just the element content
<?php
Array
(
    [index1] => a
    [index2] => b
    [value] => hello
)
?>
robbieaverill at gmail dot com 21-Jan-2015 10:32
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.
iancudanielc () gmail ! com 09-Jan-2015 08:56
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');

?>
m dot abbasian at outlook dot com 18-Oct-2014 08:58
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
*/
?>
manwe at inversion dot pl 21-Sep-2014 12:33
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');
marc dot gray at gmail dot com 29-Apr-2014 10:44
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 $array above without processing it through array_values() first.
Anonymous 02-Apr-2014 10:26
<?php
function arrayFilter($input, $callback = null) {
    foreach($input as $key => &$value) {
        if(is_array($value)) {
            $value = arrayFilter($value, $callback);
            if(is_array($value)) {
                if((bool)$value === false) unset($input[$key]);
            }
            else {
                if((bool)($callback ? $callback($value) : $value) === false) unset($input[$key]);
            }
        }
        else {
            if((bool)($callback ? $callback($value) : $value) === false) unset($input[$key]);
        }
    }
    return $input;
}
?>
avl 04-Nov-2013 12:25
nice trick:

$array_out = array_filter($array_in, function($var) use($array_other) {
            return in_array($var, $array_other) ? true : false;
});
qeremy [atta] gmail [dotta] com 02-Oct-2013 03:12
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
)
*/
?>
tomasz at trejderowski dot pl 24-Sep-2013 08:16
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.
keksnicoh at googlemail dot com 12-Aug-2013 11:01
Usefull invertation of array_filter
<?php
$data = array(...)
$noArrayData = array_filter_inverse($data, 'is_array');

/**
 * Inverts the result of the filter callback.
 * @param array $data
 * @param callable $f
 * @return array
 */
function array_filter_inverse(array $data, callable $f)
{
    return array_filter($data, function() use(&$f) {
        return ! call_user_func_array($f, func_get_args());
    });
}
?>
pavian at gmail dot com 25-Jul-2013 10:04
Regarding to strlen() related notes, if you want to filter NULL, FALSE and empty strings from the array, just omit callback function, it does the same trick (but easier).
<?php

  $clean = array_filter($array);

?>
g dot kuizinas at anuary dot com 26-Mar-2013 11:10
<?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);
?>
tx at tshwarelo-leaka dot co dot za 26-Mar-2013 09:26
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
)
Anonymous 13-Jan-2013 05:52
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' );

?>
jtreminio at gmail dot com 04-Oct-2012 07:11
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();
?>
John Erck: erck0006 at junkyo dot gmail dot com 04-Apr-2012 08:09
<?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 */
spam dot 2011 at rebell dot at 21-Nov-2011 02:28
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"
lisachenko dot it at HUMAN dot gmail dot com 22-Jul-2011 12:54
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().
rolf at example dot com 08-Nov-2010 11:06
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
)
Peter Robinett 12-Aug-2010 08:09
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.
acid24 at gmail dot com 26-Jul-2010 05:58
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)
}
Ant P. 13-Mar-2010 08:58
If you're using filter_input_array, the values will be null on failure and anything else on success. Because array_filter by default removes false, 0 and "" you need to do extra work like this:
<?php
$input_array = filter_input_array(INPUT_GET, array(
  'var1' => FILTER_VALIDATE_BOOLEAN,
  'var2' => FILTER_VALIDATE_INT
));

array_filter($input_array, function($a) { return !is_null($a) });
?>
webdesign at blackbyrd dot biz 08-Oct-2009 01:00
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)
);
mewsterus at yahoo dot com 14-Sep-2009 10:13
Here's an easy way to get a combination of keys and values, such that if you don't specify a key you will get the value, and if you do specify a key you will get the key:

<?php
$array = array('One' => 'First', 'Second', 'Third', 'Four' => 'Fourth', 'Fifth');

var_dump(array_keys($array));

$names = array_filter(array_keys($array), 'is_string') + array_values($array);
ksort($array);

var_dump($names);
?>

Outputs:

array(5) {
  [0]=>string(3) "One"
  [1]=>int(0)
  [2]=>int(1)
  [3]=>string(4) "Four"
  [4]=>int(2)
}
array(5) {
  [0]=>string(3) "One"
  [1]=>string(6) "Second"
  [2]=>string(5) "Third"
  [3]=>string(4) "Four"
  [4]=>string(5) "Fifth"
}

Without using ksort, the keys appear before the fallback values, instead of inline and appearing like they replace them, however the keys are intact (which is why ksort works) so it's only execution order.
chrisstocktonaz at gmail dot com 30-Apr-2009 09:34
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');
}
?>
niehztog 30-Dec-2008 01:27
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
romain dot lamarche at gmail dot com 11-Dec-2008 06:39
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);
  }
?>
darren at dazwin dot com 08-Oct-2008 11:44
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;
}
?>
sami 03-Oct-2008 11:11
Yes, it may remove NULLS, but it also removes anything that factors to a FALSE as well; like FALSE and ZERO. :/
Martin 04-Sep-2007 10:56
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.
leon at darkk dot net dot ru 22-May-2007 12:15
Here is a way to get customizable filter

<?php
function blablabla() {
    ....
    $new = getNewUidls();
    class UidlFilter {
        function UidlFilter($uidls) { $this->uidls = $uidls; }
        function filter($metamsg) { return in_array($metamsg['uidl'], $this->uidls); }
    }
    $msglist = array_filter($msglist, array(new UidlFilter($new), 'filter');
    ....
}
?>
Fladnag - bahatest at ifrance dot com 22-Oct-2006 09:19
If you have a form with multiple checkbox having ID element as value for selection in a list, you probably have a SQL request like :
$req="SELECT ... WHERE ID IN (".implode(',', array_keys($choices)).")";
without quote before and after choices keys because they are numeric values... but in fact, they can be string values, and a SQL injection problem.

with array_filter, you can easily filter bad values :
<?php
    $choices=array('A'=>'on', -1=>'on', 0=>'on', 1=>'on', 12=>'on', "1)or 1=1--"=>'on');
    print_r($choices);
    $choices=array_filter(array_keys($choices), 'is_numeric');
    print_r($choices);
?>
will print :
<?php
Array
(
    [A] => on
    [-1] => on
    [0] => on
    [1] => on
    [12] => on
    [1)or 1=1--] => on
)
Array
(
    [1] => -1
    [2] => 0
    [3] => 1
    [4] => 12
)
?>
marc dot vanwoerkom at fernuni-hagen dot de 05-Jul-2004 08:09
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.
Maxwel Leite 11-May-2004 08:17
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;
}
?>
Jeremy 29-Dec-2003 01:31
Here is a nice little function which will apply a callback function recursively over a multidimensional array. If the callback function returns false, then it replaces the value of the array with $filtered_ouput. This function gracefully handles objects inside of arrays (and objects within objects within arrays, etc). It is specifically designed for your callback function to process on the array key's (unlike normal array_filter which filters on the values), but it could work on the array values depending on your test criteria (YMMV).

<?PHP

function array_key_filter_multi($array, $callback, $filtered_output = "")
{
   $ret = array();
   foreach($array as $key=>$value) {
       if($callback($key,$value)) {
           if(is_array($value)) {
               $ret[$key] = array_key_filter_multi($value, $callback, $filtered_output);
           }
           elseif(is_object($value)) {
               $ret[$key] = array_key_filter_multi(get_object_vars($value), $callback, $filtered_output);
           }
           else {   
               $ret[$key]=$value;
           }
       }
       else {
           $ret[$key]=$filtered_output;
       }
   }
   return $ret;
}

?>

We use this to filter redundant data from debugging output. An example usage is:

<?

$callback_func = create_function('$key, $value', 'return ($key == "db" || $key == "smarty") ? false : true;');
echo "<PRE>" . print_r(array_key_filter_multi($_SESSION, $callback_func, "**filtered by function**"), true) . "</PRE>";

?>

Which filters all keys with "db" or "smarty" as their name (including objects which have a reference to those variables). The output of the above in a test case I did is the following:

Array
(
    [userdata] => Array
        (
            [sid] => a130e675d380e0e9fe47897922d719ac
            [not_in_db] =>
            [user_id] => 1
            [session_id] => 154
            [permissions] => 1
            [username] => tester
        )
    [systemobjects] => Array
        (
            [db] => **filtered by function**
            [smarty] => **filtered by function**
        )
)
redshift at pandora dot be 28-Jun-2003 12:01
Hi all,
Here's a function that will look trough an array, and removes the array member when the search string is found.

<?php
function array_clean ($input, $delete = false, $caseSensitive = false)
    {
    $i = 0;
    while($i < count($input))
        {
        if($delete)
            {
            if($caseSensitive)
                {
                if(!strstr($input[$i] ,$delete))
                    {
                    $return[] = $input[$i];
                    }
                }
                else
                {
                if(!stristr($input[$i], $delete))
                    {
                    $return[] = $input[$i];
                    }
                }
            }
            else
            {
            if(!empty($input[$i]))
                {
                $return[] = $input[$i];
                }
            }
        $i++;
        }
    return $return;
    }
?>

array array_clean(array input [, string needle [, boolean case sensitive]])

if needle is left empty, the function will delete the array members that have no value (this means if it's empty).
NOTE: It rebuilds the array from scratch, so keys begin with 0, like you would create a new array.

Example:
$array = array("John", "Doe", "Macy");
$array = array_clean($array, "doe", false);

print_r($array);
would return:
array
(
    [0] => John
    [1] => Macy
)

Hopes this helps someone :-)
skd2 at ece dot msstate dot edu 14-May-2003 03:24
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.
ajohnson at speakeasy dot org 27-Sep-2002 12:42
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);
 ?>
ajohnson at speakeasy dot org 17-Aug-2002 01:04
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);
?>

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