Loop through an array and take a special item from each array object and put it into a new array
<?php
$categories = get_the_category(); //Returning an array with all the categories for the current post
//if we have any categories then well copy into an array
if ($categories) {
$class_names = array();
foreach ($categories as $category) {
$class_names[] = 'cat-' . $category->slug;
}
}
?>
