Perhaps I am missing some basics here. I have an array and filtering the values with array\_filter() function. I used echo on the filter function to see if the filtered value is working or not.

```
<?php

    $columns = array(
        0 => 'ISO',
        1 => 'Country',
        2 => 'Country Code',
        3 => 'Type of number',
        4 => 'Voice Enabled',
        5 => 'SMS Enabled',
        6 => 'MMS Enabled',
        7 => 'Domestic Voice Only',
        8 => 'Domestic SMS only',
        9 => 'Price /num/month',
        10 => 'Inbound Voice price/min',
        11 =>  'Inbound SMS price/msg ',
        12 =>  'Inbound MMS price/msg ',
        13 => 'Beta Status',
        14 => 'Address Required',
    );

        echo '<pre>';
        $columns = array_filter($columns, '_filter_column_names');
        echo '</pre>';

        function _filter_column_names($column_name){
            $column_name = str_replace(' /', '_', $column_name);
            $column_name = strtolower(str_replace(array(' ', '/'), '_', trim($column_name)));

            echo $column_name.'<br>';
            return $column_name;
        }

        echo '<pre>';
        print_r($columns);
        echo '</pre>';

```

Result
------

```
iso
country
country_code
type_of_number
voice_enabled
sms_enabled
mms_enabled
domestic_voice_only
domestic_sms_only
price_num_month
inbound_voice_price_min
inbound_sms_price_msg
inbound_mms_price_msg
beta_status
address_required

Array
(
    [0] => ISO
    [1] => Country
    [2] => Country Code
    [3] => Type of number
    [4] => Voice Enabled
    [5] => SMS Enabled
    [6] => MMS Enabled
    [7] => Domestic Voice Only
    [8] => Domestic SMS only
    [9] => Price /num/month
    [10] => Inbound Voice price/min
    [11] => Inbound SMS price/msg 
    [12] => Inbound MMS price/msg 
    [13] => Beta Status
    [14] => Address Required
)

```

The resulting filtered array is **not filtered at all**. Although it seems the array values inside the filter function is filtering correctly. You can also see it live here <http://3v4l.org/SttJ3>