array_filter
FILTERS elements of an array using a callback function.
This function iterates over each value in the $array passing them to the $callback.
If the $callback = TRUE, the current value from $array is returned into the result ARRAY.
ARRAY keys are preserved.
If no $callback is supplied, all entries of $array equal to FALSE will be removed.
<?php
arr array_filter ( arr $array [, callable $callback [, int $flag = 0 ]] )
where,
$array = The ARRAY to iterate over
$callback = The callback function to be used
$flag = To determine what arguments are sent to the callback function
?>
$array
The ARRAY to iterate over.
$callback
The callback function to be used.
$flag
To determine what arguments are sente to the callback function.
| CONSTANT |
VALUE |
MEANING |
DEFAULT |
| |
0 |
Pass value as the only argument to
callback function instead |
0 |
| ARRAY_FILTER_USE_BOTH |
1 |
Pass both value and key as arguments to
callback function instead of the value |
| ARRAY_FILTER_USE_KEY |
2 |
Pass key as the only argument to
callback function instead of the value |
| ed48 |
EXERCISE
<?php
function odd ($vlu01)
{
if ($vlu01%2 == 0)
{
return $vlu01;
}
else
{
return (false);
}
}
$arr2tst01 = [ 1, 2, 3, 4, 5, 6, 8, 12, 13, 17 ];
$arrfltd01 = array_filter($arr2tst01, 'odd');
echo 'The given ARRAY<br><br>';
foreach ($arr2tst01 as $ar01a => $arr01a)
{
echo '[' . $ar01a . '] => ' . $arr01a . '<br>';
}
echo '<br><br>The ODD ELEMENTS of the given ARRAY<br><br>';
foreach ($arrfltd01 as $arf01a => $arrf01a)
{
echo '[' . $arf01a . '] => ' . $arrf01a . '<br>';
}
?>
RESULT
The given ARRAY:
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
[5] => 6
[6] => 8
[7] => 12
[8] => 13
[9] => 17
The ODD ELEMENTS of the given ARRAY:
[1] => 2
[3] => 4
[5] => 6
[6] => 8
[7] => 12
The given ARRAY keys are preserved.
EXERCISE
<?php
function even ($vlu02)
{
if ($vlu02%2 != 0)
{
return $vlu02;
}
else
{
return (false);
}
}
$arr2tst02 = [ 1, 2, 3, 4, 5, 6, 8, 12, 13, 17 ];
$arrfltd02 = array_filter($arr2tst02, 'even');
echo 'The given ARRAY<br><br>';
foreach ($arr2tst02 as $ar02a => $arr02a)
{
echo '[' . $ar02a . '] => ' . $arr02a . '<br>';
}
echo '<br><br>The EVEN ELEMENTS of the given ARRAY<br><br>';
foreach ($arrfltd02 as $arf02a => $arrf02a)
{
echo '[' . $arf02a . '] => ' . $arrf02a . '<br>';
}
?>
RESULT
The given ARRAY:
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
[5] => 6
[6] => 8
[7] => 12
[8] => 13
[9] => 17
The EVEN ELEMENTS of the given ARRAY:
[0] => 1
[2] => 3
[4] => 5
[8] => 13
[9] => 17
The given ARRAY keys are preserved.
EXERCISE
<?php
$arr2tst03 = [ 1 => 'string', 2 => NULL, 3 => '', 4 => ' ',
5 => false, 6 => true, 7 => number_format(6.345, 3) ];
$arrfltd03 = array_filter($arr2tst03);
echo 'The given ARRAY<br><br>';
foreach ($arr2tst03 as $ar03a => $arr03a)
{
echo '[' . $ar03a . '] => ' . $arr03a . '<br>';
}
echo '<br><br>FALSE,
NULL
or
EMPTY STRING,
WILL BE REMOVED
from the given ARRAY<br><br><pre>';
var_dump($arrfltd03);
echo '</pre>';
?>
RESULT
The given ARRAY:
[1] => string
[2] =>
[3] =>
[4] =>
[5] =>
[6] => 1
[7] => 6.345
FALSE, NULL or EMPTY STRING,
WAS REMOVED from the given ARRAY:
array(4) {
[1]=>
string(6) "string"
[4]=>
string(1) " "
[6]=>
bool(true)
[7]=>
string(5) "6.345"
}
The given ARRAY keys are preserved.
EXERCISE
<?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, 0);
$array3 = array(TRUE, FALSE, NULL);
echo "Odd :<br><pre>";
var_dump(array_filter($array1, "odd"));
var_dump(array_filter($array2, "odd"));
var_dump(array_filter($array3, "odd"));
echo "</pre>Even:<br><pre>";
var_dump(array_filter($array1, "even"));
var_dump(array_filter($array2, "even"));
var_dump(array_filter($array3, "even"));
echo '<br>';
var_dump(array_filter(array()));
echo '</pre>';
?>
EXERCISE
<?php
/*
* Passing different types of array as 'input' argument.
*/
function always_false($input)
{
return false;
}
// callback function returning always true
function always_true($input)
{
return true;
}
echo "Testing array_filter() : usage variations -
<br>- different types of array for 'input' argument.<br>";
// different types of 'input' array
$input_values = array(
array(0, 1, 2, -1, 034, 0X4A),
// integer values
array(0.0, 1.2, 1.2e3, 1.2e-3),
// float values
array('value1', "value2", '', " ", ""),
// string values
array(true, false, TRUE, FALSE),
// bool values
array(null, NULL),
// null values
array(1 => 'one', 'zero' => 0, -2 => "value"),
//associative array
array("one" => 1, null => 'null', 5.2 => "float",
true => 1, "" => 'empty'),
// associative array with different keys
array(1 => 'one', 2, "key" => 'value')
// combinition of associative and
// non-associative array
);
// loop through each element of 'input' with default callback
for($count = 0; $count < count($input_values); $count++)
{
echo "<br><br><b>Iteration: ".($count + 1). "</b><br><br>";
var_dump( array_filter($input_values[$count]) );
echo '<br><br>';
var_dump( array_filter($input_values[$count],
'always_true') );
echo '<br><br>';
var_dump( array_filter($input_values[$count],
'always_false') );
}
?>
EXERCISE
<?php
/*
* Passing different types of
* callback functions to array_filter()
* with parameters and return
* without parameter and with return
* with parameter and without return
* without parameter and without return
*/
echo "Testing array_filter() : usage variation -
<br>- different 'callback' functions.";
// Initialize variables
$input = array(0, -1, 2,
3.4E-3,
'hello', "value",
"key" => 4,
'null' => NULL);
function callback1()
{
return 1;
}
echo "<br><br>Without parameter and with return:<br>";
var_dump( array_filter($input, "callback1") );
// callback function with parameter
// and without return value
function callback2($input)
{
}
echo "<br><br>With parameter and without return:<br>";
var_dump( array_filter($input, "callback2") );
function callback3()
{
}
echo "<br><br>Without parameter and return:<br>";
var_dump( array_filter($input, "callback3") );
// callback function with parameter
// and with return value
function callback4($input)
{
if($input > 0 ) {
return true;
}
else {
return false;
}
}
echo "<br><br>With parameter and return:<br>";
var_dump( array_filter($input, "callback4") );
?>
EXERCISE
<?php
/*
* With default callback function argument,
* array_filter() removes elements which
* are interpreted as false
* Here Testing all the false array
* element possibilities
*/
function always_true($input)
{
return true;
}
// callback function always_false
function always_false($input)
{
return false;
}
echo "Testing array_filter() : usage variations -
<br>- different false elements in 'input'.<br><br>";
// unset variable
$unset_var = 10;
unset($unset_var);
// empty heredoc string
$empty_heredoc =<<<EOT
EOT;
// input array with different false elements
$input = array(
false,
False,
'',
"",
0,
0.0,
null,
NULL,
"0",
'0',
array(),
!1,
1==2,
$empty_heredoc,
@$unset_var,
@$undefined_var,
);
// With default callback function
var_dump( array_filter($input) );
echo '<br><br>';
// With callback function which returns always true
var_dump( array_filter($input, 'always_true') );
echo '<br><br>';
// With callback function which returns always false
var_dump( array_filter($input, 'always_false') );
?>
EXERCISE
<?php
/*
* Passing 'input' array which contains
* elements as reference to other data
*/
echo "Testing array_filter() : usage variations -
<br>- 'input' containing references.<br><br>";
function callback($input)
{
if($input > 5) {
return true;
}
else {
return false;
}
}
// initializing variables
$value1 = array(1, 2, 8);
$value2 = array(5, 6, 4);
echo 'The given $value1:<br>';
var_dump($value1);
echo '<br><br>The given $value2:<br>';
var_dump($value2);
$input = array(&$value1, 10, &$value2, 'value');
echo '<br><br>The $input:<br>';
var_dump($input);
echo '<br><br><br>After array_filter($input, \'callback\'):<br>';
// with 'callback' argument
var_dump( array_filter($input, 'callback') );
echo '<br><br>After array_filter($input):<br>';
// with default 'callback' argument
var_dump( array_filter($input) );
?>
EXERCISE
<?php
/*
* Passing different anonymous
* callback functions with passed
* by value and reference arguments
*/
echo "Testing array_filter() : usage variations -
<br>- Anonymous callback functions.<br><br>";
$input = array(0, 1, -1, 10, 100, 1000, 'Hello', null);
// anonymous callback function
echo "With regular parameter and statement:<br>";
var_dump( array_filter($input,
function($input) { return ($input > 1); }) );
// anonymous callback function with null argument
echo "<br><br>With null argument:<br>";
var_dump( array_filter($input,
function() { return true; }) );
// anonymous callback function with
// argument and null statement
echo "<br><br>With regular argument
and null statement:<br>";
var_dump( array_filter($input,
function($input) { }) );
?>
EXERCISE
<?php
/*
* callback functions are expected
* to return bool value for array_filter()
* here testing callback functions for
* return values other than bool
*/
echo "Testing array_filter() : usage variations -
<br>- callback function with different return values.<br><br>";
$input = array(0, 1, -1, 10, 100, 1000, 'Hello', null, true);
function callback1($input)
{
return 5;
}
echo "callback function with int return value:<br>";
var_dump( array_filter($input, 'callback1') );
// float as return value
function callback2($input)
{
return 3.4;
}
echo "<br><br>callback function with float return value:<br>";
var_dump( array_filter($input, 'callback2') );
// string as return value
function callback3($input)
{
return 'value';
}
echo "<br><br>callback function with string return value:<br>";
var_dump( array_filter($input, 'callback3') );
// null as return value
function callback4($input)
{
return null;
}
echo "<br><br>callback function with null return value:<br>";
var_dump( array_filter($input, 'callback4') );
// array as return value
function callback5($input)
{
return array(8);
}
echo "<br><br>callback function with array as return value:<br>";
var_dump( array_filter($input, 'callback5') );
?>