Related posts not working in the index

Question

I use this code in the single.php and it works perfectly. But in the index.php nothing appears.

single.php:

<div id="relatedposts">
<?php $orig_post = $post;
global $post;
$categories = get_the_category($post->ID);
if ($categories) {
$category_ids = array();
foreach($categories as $individual_category) $category_ids[] = $individual_category->term_id;
$args=array(
'category__in' => $category_ids,
'post__not_in' => array($post->ID),
'posts_per_page'=> 4, // Number of related posts that will be shown.
'caller_get_posts'=>1
);
$my_query = new wp_query( $args );
if( $my_query->have_posts() ) {
while( $my_query->have_posts() ) {
$my_query->the_post();?>
<div class="related">
<a href="<? the_permalink()?>" title="<?php the_title(); ?>">
<?php if(has_post_thumbnail()) {
the_post_thumbnail(array(100,100), array( 'class' => 'relthumb' ));
} else {echo '<img class="relthumb" src="'.get_bloginfo('template_url').'/images/noimgrelated.png" />';
}?></a>
<div class="title"><a href="<? the_permalink()?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a></div>
</div><!-- /* .related -->
<?
}
echo '';
}
}
$post = $orig_post;
wp_reset_query(); ?>
</div><!-- /* .relatedposts -->

How can I make work in index? Sorry my english.

Answer 1

That code should work. I just tested in my own index.php and it worked. Are you sure you're looking at the index.php file. Sometimes WP actually pulls a different template: For more info, see WP template hierarchy diagram. To test what template you're seeing, place this code in your functions.php file temporarily:

add_action('wp_head', 'show_template');
    function show_template() {  
      global $template;
      echo '<span style="color: #000; z-index: 10000; position: absolute;">' . $template . '</span>';
    }