数组 函数
在线手册：中文 英文
PHP手册

array_filter

(PHP 4 >= 4.0.6, PHP 5)

array_filter — 用回调函数过滤数组中的单元

说明

array array_filter ( array $input [, callback $callback ] )

array_filter() 依次将 input 数组中的每个值传递到 callback 函数。如果 callback 函数返回 TRUE，则 input 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。

Example #1 array_filter() 例子

<?php
function odd($var)
{
    return($var % 2 == 1);
}

function even($var)
{
    return($var % 2 == 0);
}

$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
)

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，此函数的行为没有定义。

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

Example #2 array_filter() 无 callback

<?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
)

参见 array_map()，array_reduce() 和 array_walk()。

参数

input

The array to iterate over

callback

The callback function to use

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

返回值

Returns the filtered array.

范例

Example #3 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(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 #4 array_filter() without callback

<?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
)

注释

Caution

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

参见

数组 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 用回调函数过滤数组中的单元

用户评论:

John Erck: erck0006 at junkyo dot gmail dot com (05-Apr-2012 04:09)

<?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 */

PHPannonces (18-Mar-2012 11:03)

// Suppression des entrées vides du tableau et réindexation numérique du tableau
// Remove blank entries in the table and reindexing numeric table
$array = array('tomate', '', 'pomme', 'melon', 'cerise', '', '', 'banane');
print_r(array_values(array_filter($array)));

geoff dot williams dot junk at gmail dot com (28-Jan-2012 02:14)

Improving on the array_filter_recursive function by romain dot lamarche at gmail dot com

<?php

function array_filter_recursive($array, $callback = null) {
    foreach ($array as $key => & $value) {
        if (is_array($value)) {
            $value = array_filter_recursive($value, $callback);
        }
        else {
            if ( ! is_null($callback)) {
                if ( ! $callback($value)) {
                    unset($array[$key]);
                }
            }
            else {
                if ( ! (bool) $value) {
                    unset($array[$key]);
                }
            }
        }
    }
    unset($value);

    return $array;
}

?>

spam dot 2011 at rebell dot at (21-Nov-2011 10:28)

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 08:54)

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().

noonesvk at gmail dot com (04-May-2011 10:01)

Hi all,

I made a simple reindex & filter function.

reindex( array $input, [ $blacklist = array() ] )

This function is working only with array that has keys in INTEGER.

<?php

function reindex(array $source, $blacklist = array())
{
    $i = 0;
    foreach ($source as $key => $val) {
        if ($key != $i) {
            unset($source[$key]);
            $source[$i] = $val;
        }
       
        $i++;
    }
   
    foreach ($source as $key => $val) {
        foreach ($blacklist as $var) {
            if ($val === $var) {
                unset($source[$key]);   
                $source = reindex($source, $blacklist);
            }
        }
    }
   
    return $source;
}

// Examples:

// Create a simple array
$input = array(1 => 'red', 3 => 'green', 5 => 'blue', 7 => TRUE, 9 => FALSE, 11 => NULL);

// NOTE: If you have an array (look above) and your blacklist will look like this: array(TRUE, FALSE, NULL)
//          Filter will delete array keys with value TRUE, FALSE or NULL
$blacklist = array(TRUE, FALSE, NULL);

// Output is: Array ( [0] => red [1] => green [2] => blue )
print_r( reindex($input, $blacklist) );

?>

If you don't want to filter array by keys in blacklist, just use this prototype: reindex( array $input ), it should be fine. :)

If you guys have question, feel free to contact me. Have a nice day.

breich at reich-consulting dot net (15-Dec-2010 07:19)

I built the following array_remove_keys() function to
remove one or more keys from an array.

<?php
 
function array_remove_keys($array, $keys = array()) {
 
    // If array is empty or not an array at all, don't bother
    // doing anything else.
    if(empty($array) || (! is_array($array))) {
        return $array;
    }
 
    // If $keys is a comma-separated list, convert to an array.
    if(is_string($keys)) {
        $keys = explode(',', $keys);
    }
 
    // At this point if $keys is not an array, we can't do anything with it.
    if(! is_array($keys)) {
        return $array;
    }
 
    // array_diff_key() expected an associative array.
    $assocKeys = array();
    foreach($keys as $key) {
        $assocKeys[$key] = true;
    }
 
    return array_diff_key($array, $assocKeys);
}
 
// Example:
$data = array(
    'name' => 'Brian',
    'address1' => '98 Market St.',
    'address2' => 'N/A'
);
 
// Output before array_remove_keys()
var_dump($data);
 
// Remove address2 key.
$data = array_remove_keys($data, 'address2');
 
// Output after array_remove_keys()
var_dump($data);
 
/* Output:
 
array(3) {
  ["name"]=>
  string(5) "Brian"
  ["address1"]=>
  string(13) "98 Market St."
  ["address2"]=>
  string(3) "N/A"
}
array(2) {
  ["name"]=>
  string(5) "Brian"
  ["address1"]=>
  string(13) "98 Market St."
}
*/
?>

rolf at example dot com (08-Nov-2010 07:06)

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 04:09)

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 01:58)

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 04:58)

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 09:00)

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 06:13)

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.

mchargue at usc dot edu (07-Aug-2009 10:34)

Wanting to pass an additional to parameter to the callback function?  This worked for me, there's probably another way to accomplish this task but just so you see how it can be done.  (I actually used this technique to strip old dates out of an array) :

<?php
//define in global scope so functions can access
$var_to_pass = null;

function myfilter($input_var_outer,$param) {

    global $var_to_pass;
    $var_to_pass = $param;

    function mycallback($input_var_inner) {
      global $var_to_pass;
      return ($input_var_inner>$var_to_pass) ? true : false;
    }

    $return_arr = array_filter($input_var_outer,'mycallback');
    //re-key if you want
    $return_arr = array_merge(array(),$return_arr);
    return $return_arr;

}

$min = 5;
$a = array(1,3,5,7,9);

//remove elements from array that are not greater than $min
$a = myfilter($a,$min);

echo "<pre>";
print_r($a);
echo "</pre>";
?>

--

Output:
Array
(
    [0] => 7
    [1] => 9
)

chrisstocktonaz at gmail dot com (30-Apr-2009 05:34)

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');
}
?>

nat at fishtrap dot co dot uk (18-Mar-2009 05:28)

One of the nice things about this function is that you can a standard php function such as is_string

e.g.
<?php

$input =array(1 , '2', 'three', array('sausages'));

$result = array_filter($input ,'is_string');

print_r($result);

?>

Result will be

Array
(
    [1] => 2
    [2] => three
)

Craig (07-Mar-2009 06:34)

I wanted a function to keep the values that were filtered out and return them separately. Basically, split the array by some callback. I wrote this for the job:

<?php
function array_split($input, &$trues, &$falses, $compare)
{
    while (($item = array_pop($input)) != NULL)
    {
        if ($compare($item)) $trues[] = $item;
        else $falses[] = $item;
    }
}
?>

very simple, something I would think would be standard, and array_filter would amount to discarding the falses.

marijnk at NOSPAM dot gwobbel dot com (05-Mar-2009 10:16)

I was looking for a function that could filter values from an array using a regular expression pattern supplied, based on leon at darkk dot net dot ru I created the following:

Description:
Return array of matching values from array using regular expression.
<?php
class array_ereg {
    function array_ereg($pattern) { $this->pattern = $pattern; }
    function ereg($string) {
        return ereg($this->pattern, $string);
    }
}
?>
 Usage :
<?php
      $matches = array_filter($subject, array(new array_ereg($pattern), 'ereg'));
?>
 Example:
 <?php
     $subject = array ("Thumbs.db", "image001.png", "image001.jpg", "image002.png");
     print_r(array_filter($subject, array(new array_ereg("image[0-9]{3}\.png"), 'ereg')));
?>
 Outputs:
     Array ( [1] => image001.png [3] => image002.png )

niehztog (30-Dec-2008 09:27)

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 02:39)

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 07:44)

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 (04-Oct-2008 07:11)

Yes, it may remove NULLS, but it also removes anything that factors to a FALSE as well; like FALSE and ZERO. :/

quecoder at gmail (27-Aug-2008 11:00)

// my implementation for array_filter 

function my_array_filter($array,$function,$preserve=true)
        {   
            $return = array();
            foreach ($array as $k=>$v)
                {
                    if($function($v)==true) $return[$k]=$v;
                }
                if($preserve) return $return;
                else return array_values($return);
        }
       
function odd($value)
        {
            return ($value & 1);
        }       
   
$oddonly = array (1,2,3,4,5,6,7,8,9);
print_r(my_array_filter($oddonly,'odd',1));   

//output    
//Array ( [0] => 1 [2] => 3 [4] => 5 [6] => 7 [8] => 9 )

//Khaled Mohammed

WASD (29-Jul-2008 12:53)

You can easily delete all NULL elements from array with following statement:

<?php
$arr = array_filter($arr);
?>

Joan Garnet (04-Jan-2008 02:47)

Be careful with this function as it preserves array indexes after applying the filter:

<?php
function f( $item ){
    return $item < 50;
}
print_r( array_filter(array( 10, 100, 20 ),"f") );
/* OUTPUT
Array
(
    [0] => 10
    [2] => 20
)*/
?>

You can easily reassign indexes like this:

<?php
function f( $item ){
    return $item < 50;
}
print_r( array_values(array_filter(array( 10, 100, 20 ),"f")) );
/* OUTPUT
Array
(
    [0] => 10
    [1] => 20
)*/
?>

nospam at jcornelius dot com (23-Oct-2007 07:51)

Don't forget that using callbacks in a class requires that you reference the object name in the callback like so:

<?php

$newArray = array_filter($array, array($this,"callback_function"));

?>

Where "$this" is the reference to your object.

Martin (04-Sep-2007 06:56)

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.

Hayley Watson (29-Aug-2007 11:49)

Just a simplification of my function from last month.

<?php
function partition($input, $callback=null)
{
    if(is_null($callback))
        $true = array_filter($input);
    else
        $true = array_filter($input, $callback);

    $false = array_diff_key($input, $true);
}
?>

Hayley Watson (27-Jul-2007 03:31)

Here is my own version of Renee Sarsoo's array_split() function; given an array and a callback it returns two arrays, in which the first contains elements that passed the filter and the second contains elements that didn't. (If no callback is passed, the first array contains the nonempty elements, as you'd get from array_filter() if you don't give it a callback). Array keys are preserved.

<?php
function partition($input, $callback=null)
{
    static $not_empty=null;
    if(is_null($not_empty))
        $not_empty = create_function('$o', 'return !empty($o);');
    if(is_null($callback)) $callback = $not_empty;

    $true = array_filter($input, $callback);
    $false = array_diff_key($input, $true);

    return array($true, $false);
}
?>

Rene Saarsoo (09-Jul-2007 02:07)

Sometimes you want to do something with elements you have filtered out and something else with other elements. So instead of filtering elements out to one array you would like to split array into two parts:
<?php
/**
 * Splits array into two arrays using a callback function
 *
 * It is like array_filter(), but instead of one array, two arrays are returned:
 * first one with elements for which the callback function evaluates to true,
 * and second one, for which it evaluates to false.
 *
 * If no callback is supplied, all entries of input equal to FALSE will be removed.
 *
 * Array keys are preserved.
 *
 * @param $callback the callback function to use
 * @return array(truth_array, false_array)
 */
function array_split($input, $callback=null) {
    $callback = isset($callback) ? $callback : create_function('$x', 'return $x == true;');
   
    $true = array();
    $false = array();
    foreach ($input as $key => $value) {
        if (call_user_func($callback, $value)) {
            $true[$key] = $value;
        }
        else {
            $false[$key] = $value;
        }
    }
   
    return array($true, $false);
}
?>

leon at darkk dot net dot ru (22-May-2007 08:15)

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');
    ....
}
?>

klaproth at creative-mindworks dot de (23-Oct-2006 03:13)

As long as the array's keys are irrelevant, there is a simple way to remove blank values from the array, after filtering has been applied. The following example is used to remove all strings from an array that have a length of less than 4 characters.

<?php
function validElement($element) {
    return strlen($element) > 3;
}

$filtered_array = array_values(array_filter($input_array, "validElement"));
?>

Fladnag - bahatest at ifrance dot com (22-Oct-2006 05:19)

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
)
?>

ydotzhangatwriwindberdotorg (17-Jan-2006 09:57)

I have written a function that will filter an array by the frequency of
element value in the array.  This may be useful to some people.

<?php
/////////////////////////////////////////////////////////////////
//    Filter an array by value freguebcy
//    Input: $array
//    cut-off: $frequency (>=1)
//    result option option: 1=$frequency and higher
//          0=$frequency only
//          -1=$frequency and lower
/////////////////////////////////////////////////////////////////
function filter_array($array, $frequency = 2, $include = 1){
    $freg = array_count_values($array);
    if($frequency<1){
       print "** frequency cut-off should be >= 1! **\n";
       return false;
    }
    foreach($freg as $k => $v){
        if($include == 0){
            if($frequency != $v){
                $freg[$k] = 0;
            }
        }elseif($include > 0){
            if($frequency > $v){
                $freg[$k] = 0;
            }
        }else{
            if($frequency < $v){
                $freg[$k] = 0;
            }
        }
    }
    $filtered = array_filter($freg);
    $values = array_keys($filtered);
    return array_intersect($array,$values);
}
?>

xert (26-Apr-2005 01:14)

According to a simple test with array_filter($array) and array_diff($array, array('')) is array_filter 2.5 times faster than array_diff when deleting empty entries.

marc dot vanwoerkom at fernuni-hagen dot de (05-Jul-2004 04:09)

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 04:17)

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;
}
?>

steven at xinu dot org (23-Feb-2004 08:39)

The anonymous fellow a few posts up was trying to illustrate how to use the array_filter() function with class methods but confused things a bit. Here's a cleaner example:

<?php
class testclass
{
    function testclass()
    {
        // define the numbers array
        $numbers = array(1, 2, 3, 4, 5, 6);

        // pull out the odd numbers
        $odd = array_filter($numbers, array($this, "odd"));

        // pull out the even numbers
        $even = array_filter($numbers, array($this, "even"));
    }

    function odd($var)
    {
        return($var % 2 == 1);
    }

    function even($var)
    {
        return($var % 2 == 0);
    }
}
?>

Jeremy (29-Dec-2003 09:31)

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 08:01)

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 11:24)

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.

(11-Feb-2003 10:47)

You cannot do this:
$non_empty_array = array_filter($original_array, 'empty');
Since empty() is not a function but a language construct. (http://www.php.net/manual/en/function.empty.php)

ajohnson at speakeasy dot org (27-Sep-2002 08:42)

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 09:04)

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);
?>

(13-Jun-2002 12:14)

I was looking for a function able to take some values out of an array iteratively, and found array_filter very useful although i had some trouble figuring out the proper syntax...

<?php
class someclass {
    var $current;

    /** this is our iterative function */
    function main ($variable,$array){
        if (end test){
            return true;
        }
        $variable= some treatment...
        if (in_array($variable, $array)){
             $this->current=something...($variable);
            // this is the not-well-documented part
            $array=$array_filter($array, array($this, "array_reduce");
        }
        $this->main($variable, $array);
    }
   
    /** this is the function used to filter */
    function reduce_list($var){
        return ($var!=$this->current);
    }
}
?>

sam,pointsystems,com (21-Feb-2002 01:12)

Here's a good function to filter multidimensional arrays:

<?php
function array_filter_multi($input, $filter="", $keepMatches=true) {
        if (!is_array($input))
                return ($input==$filter xor $keepMatches==false) ? $input : false;
        while (list ($key,$value) = @each($input)){
                $res = array_filter_multi($value, $filter,$keepMatches);
                if ($res !== false)
                        $out[$key] = $res;
        }
        return $out;
}
?>

Default behavior is to remove blanks from a multi-dimensional array, but you can filter out any string (arg #2) with a positive or negative filter (arg #3).