PHP array_filter() Function

The PHP array_filter() function filters elements of an array using a callback function. This function iterates over each value in the array passing them to the callback function. If the callback function returns true, the current value from array is returned into the result array.

Note: This function preserves the array key, therefore may result in gaps if the array was indexed. The result array can be reindexed using the array_values() function.

Syntax

array_filter(array, callback, mode)

Parameters

`array`	`Required.` Specify the array to iterate over.
`callback`	`Optional.` Specify the callback function to use. If no callback function is supplied, all empty entries of array will be removed.
`mode`	`Optional.` Specify flag which determines what arguments are sent to callback: ARRAY_FILTER_USE_KEY - pass key as the only argument to callback instead of the value. ARRAY_FILTER_USE_BOTH - pass both value and key as arguments to callback instead of the value. Default is 0 which will pass value as the only argument to callback instead.

Return Value

Returns the filtered array.

Exceptions

NA.

Example:

The example below shows the usage of array_filter() function.

<?php
function odd($x) {
  //returns true when x is odd, 
  //else returns false
  return $x & 1;
}

function even($x) {
  //returns true when x is even, 
  //else returns false
  return !($x & 1);
}

$Arr1 = array(10, 11, 12, 13, 14, 15, 16);
$Arr2 = array('a' => 1, 'b' => 2, 'c' => 3, 
              'd' => 4, 'e' => 5, 'f' => 6);

echo "Even values from Arr1\n";
//filtering only even values from Arr1
print_r(array_filter($Arr1, "even"));

echo "\nOdd values from Arr2\n";
//filtering only odd values from Arr2
print_r(array_filter($Arr2, "odd"));
?>

The output of the above code will be:

Even values from Arr1
Array
(
    [0] => 10
    [2] => 12
    [4] => 14
    [6] => 16
)

Odd values from Arr2
Array
(
    [a] => 1
    [c] => 3
    [e] => 5
)

Example: array_filter() without callback function

If no callback function is supplied, all empty entries of the array is removed as shown in the example below:

<?php
$Arr = array(0 => 'red', 
             1 => false, 
             2 => -1, 
             3 => '0', 
             4 => null, 
             5 => '',
             6 => 0);

//after removing empty entries
print_r(array_filter($Arr));
?>

The output of the above code will be:

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

Example: array_filter() with mode parameter

The mode parameter can be used to determine what arguments are sent to callback function. Consider the example below:

<?php
function mode_key($k) {
  return ($k%2 == 0);
}

function mode_value_key($v, $k) {
  return ($v%2 == 0) && ($k%2 == 0);
}

$Arr = array(10, 12, 15, 17, 20, 22, 25);

//selecting only even keys
print_r(array_filter($Arr, 'mode_key', 
        ARRAY_FILTER_USE_KEY));

echo"\n";
//selecting even keys and values
print_r(array_filter($Arr, 'mode_value_key', 
        ARRAY_FILTER_USE_BOTH));
?>

The output of the above code will be:

Array
(
    [0] => 10
    [2] => 15
    [4] => 20
    [6] => 25
)

Array
(
    [0] => 10
    [4] => 20
)

❮ PHP Array Reference