Wordpress: Show only TOP level categories

Here is my script to get top level category names from within the loop. This will include top level categories that just have a child category checked, and are not explicitly checked themselves.

<?php
    $categories = get_the_category();
    $topcats = array();
    foreach ($categories as $cat) {
        if ($cat->parent != 0) $cat = get_term($cat->parent, 'category');
        $topcats[$cat->term_id] = '<a href="/category/' . $cat->slug . '">' . $cat->name . '</a>';
    }
    echo implode(', ', $topcats);
?>

soju post is very helpful, for to get category only 1 level subcategory we should just pass the category id that has subcategories . But if the subcategory have no any post then it doesnot shows but subcategory subcategory consist the post so add 'hide_empty' => 0, in the above condition it will look like

$args = array(
'taxonomy' => 'categories',
'parent' => 7,
'hide_empty' => 0,
);

There is no depth argument for get_categories(), you should try :

$args = array(
  'orderby' => 'name',
  'parent' => 0
);

parent : (integer) Display only categories that are direct descendants (i.e. children only) of the category identified by its ID. This does NOT work like the 'child_of' parameter. There is no default for this parameter. [In 2.8.4]

Read more : http://codex.wordpress.org/Function_Reference/get_categories#Get_only_top_level_categories