Array_filter and empty()

Question

Warning: array_filter() expects parameter 2 to be a valid callback, function \'empty\' not found or invalid function name....

Why is e

Answer 1

I think a better solution exist and I found it reading the doc about array_filter

See this comment : https://www.php.net/manual/fr/function.array-filter.php#111091

<?php

// removes all NULL, FALSE and Empty Strings but leaves 0 (zero) values
$result = array_filter( $array, 'strlen' );

?>

I only allow myself to post it because I think it's a very elegant solution.

Also, as array_filter itself already filter null or false value as a default callback, this code work too :

$array = array('apple', '', 'watermelon');
var_dump(array_filter($array));

----
Output : 
array(2) { [0]=> string(5) "apple" [2]=> string(10) "watermelon" }

Answer 2

Answer

empty() is not a function but a language construct and array_filter() can only accept a function as its callback.

This is given as a small note on the manual page:

Note: Because this is a language construct and not a function, it cannot be called using variable functions

Work around

To work around this you can wrap empty in another function for example:

function empty_test($val) {
    return empty($val);
}

And then call it like so:

$arr = array_filter($arr, 'empty_test');

Answer 3

empty() is a language construct, and not a true function in terms of PHP, so you can't pass its name as an argument to functions like array_filter() and call_user_func_array().

From the manual:

Note: Because this is a language construct and not a function, it cannot be called using variable functions

For a workaround, just wrap it in another user-defined function; see Treffynnon's answer.

Answer 4

See the documentation page on empty():

Note: Because this is a language construct and not a function, it cannot be called using variable functions

So basically empty() is not a function, and because callback must be a function, empty() can not be passed as callback.

But you can create callback that may use empty(). The following should work in PHP > 5.3:

$arr = array_filter($arr, function($var){
    return empty($var);
});

In PHP < 5.3 you will need to create similar function first and then pass it to the array_filter().

Did it help?

Answer 5

You can use just array_filter() function without callback:

Remove empty array elements in PHP

$arr = array("PHP", "HTML", "CSS", "", "JavaScript", null, 0);
print_r(array_filter($arr)); // removing blank, null, false, 0 (zero) values

Result:

Array
(
    [0] => PHP
    [1] => HTML
    [2] => CSS
    [4] => JavaScript
)