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PHP : Function Reference : Array Functions : array_filter

array_filter

Filters elements of an array using a callback function (PHP 4 >= 4.0.6, PHP 5)
array array_filter ( array input [, callback callback] )

Example 245. array_filter() example

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<?php
function odd($var)
{
   return($var & 1);
}

function even($var)
{
   return(!($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"));
?>

The above example will output:

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

Example 246. array_filter() without callback

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<?php

$entry = array(
            0 => 'foo',
            1 => false,
            2 => -1,
            3 => null,
            4 => ''
         );

print_r(array_filter($entry));
?>

The above example will output:

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Array
(
   [0] => foo
   [2] => -1
)

Code Examples / Notes » array_filter

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)

martin
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.
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.

skd2
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.

steven
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);
}
}
?>

rene saarsoo
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);
}
?>

marc dot vanwoerkom
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.

hayley watson
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);
}
?>

fladnag - bahatest
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
)
?>

ajohnson
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...
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);
   }
}

ydotzhangatwriwindberdotorg
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.
/////////////////////////////////////////////////////////////////
// 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);
}

redshift
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 :-)

sam,pointsystems,com
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).

hayley watson
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);
}
?>

leon
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');
   ....
}
?>

jeremy
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**
       )
)

maxwel leite
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;
}
?>

nospam
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.

timo
Do not use this function to delete known values from an array; array_diff() does the job much easier.
For example, to delete all empty strings from an array:
<?php
   $arr = array_diff($arr, array(''));
?>

ajohnson
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);
?>

klaproth
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"));
?>

xert
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.

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