If in subcategory of a category?

Try this:

<?php
// if a category view see if category is id=6 or 'direct child' of 6
if ( is_category() ) {
  $cat = get_query_var('cat');
  $args = array(
    'include' => $cat,
	  'hide_empty' => 0
	  );
  $categories = get_categories($args);
  if ( ($cat == 6) || ($categories[0]->category_parent == 6) ) {
    echo 'you are viewing cat 6 or one of the DIRECT child';
  }
}
?>

This almost solved my problem. When it’s alone it works, but when I put two of them in a row the second one wont work. Like this:

<?php // The first works works.
           if ( is_category() ) {
 			$cat = get_query_var('cat');
 			$args = array(
 			'include' => $cat,
 			'hide_empty' => 0
 			);
 			$categories = get_categories($args);
 			if ( ($cat == 1) || ($categories[0]->category_parent == 1) ) {
 			wp_list_categories('child_of=1&orderby=name&order=DESC&title_li=');
 			}

			} elseif // The second wont work.
             ( is_category() ) {
 			$cat = get_query_var('cat');
 			$args = array(
 			'include' => $cat,
 			'hide_empty' => 0
 			);
 			$categories = get_categories($args);
 			if ( ($cat == 18) || ($categories[0]->category_parent == 18) ) {
 	              wp_list_categories('child_of=18&orderby=name&order=DESC&title_li=');
 			} ?>

Or in_category or is_category wont work after it.

Thanks Michael! This was so far very helpful!

You wouldn’t really need that 2nd set of code–

<?php
if ( is_category() ) {
  $cat = get_query_var('cat');
  $args = array(
    'include' => $cat,
    'hide_empty' => 0
    );
  $categories = get_categories($args);
  if ( ($cat == 1) || ($categories[0]->category_parent == 1) ) {
    $child_of='child_of=1';
    } elseif ( ($cat == 18) || ($categories[0]->category_parent == 18) ) {
    $child_of='child_of=18';
    } else {
    $child_of='';
  }
  if ($child_of) {
    wp_list_categories($child_of .'&orderby=name&order=DESC&title_li=');
  }
}
?>

Thanks again Michael! That solved it for me ??

One small issue arise while testing this.

The following doesn’t work in single.php file but works in archive and category templates.

If this post is in subcategory x get the sidebar-x.php.

<?php
if ( is_category() ) {
  $cat = get_query_var('cat');
  $args = array(
    'include' => $cat,
    'hide_empty' => 0
    );
  $categories = get_categories($args);
  if ( ($cat == 1) || ($categories[0]->category_parent == 1) ) {
    include(TEMPLATEPATH . '/sidebar.php');
    } elseif ( ($cat == 41) || ($categories[0]->category_parent == 41) ) {
    include(TEMPLATEPATH . '/sidebar02.php');
    } elseif ( ($cat == 18) || ($categories[0]->category_parent == 18) ) {
    include(TEMPLATEPATH . '/sidebar03.php');
    } else {
    get_sidebar();
  	}
}
?>

Is there a way around this?

Thanks again! It’s been so helpful so far!

You’ll want to use the is_single() conditional. Also you need to get the categories (note plural) from the post itself…this example uses the FIRST category found on the post

if ( is_single() ) {
  $cats = wp_get_post_categories($post->ID);
  if ($cats) {
    $cat = $cats[0];
  }
  $args = array(
    'include' => $cat,
    'hide_empty' => 0
  );
}

Just to clarify (there was some confusion in another thread about this) — you have to actually copy the definition of the post_is_in_descendant_category function mentioned in the Codex before you use it — it doesn’t come with WordPress. ??