Advanced Filter for Tag Cloud Widget Css Classes

tag cloud widget advanced color styling

The default tag cloud widget does not offer a lot of formatting possibilities, partly because it only outputs one css class with a reference to the tag ID.
It uses an inline style, which outputs the font-size, to distinguish the tags according the number of post they belong to.

This filter function is coded to add a css class with the tag slug .tag-slug-{slug} and with a rounded tag size .tag-size-{number}, and to remove the inline style.

add_filter ( 'wp_tag_cloud', 'tag_cloud_widget_advanced_classes' );  

function tag_cloud_widget_advanced_classes( $taglinks ) { 
	$tags = explode('</a>', $taglinks);
	$regex1 = "#(.*tag-link[-])(.*)(' title.*)#e";         
	$regex2 = "#(.*style='font-size:)(.*)((pt|px|em|pc|%);'.*)#e"; 
	$regex3 = "#(style='font-size:)(.*)((pt|px|em|pc|%);')#e";         
	$regex4 = "#(.*class=')(.*)(' title.*)#e";         
	foreach( $tags as $tag ) {         
		$tag = preg_replace($regex1, "('$1$2 tag-slug-'.get_tag($2)->slug.'$3')", $tag ); //add .tag-slug-{slug} class   
		$size = preg_replace($regex2, "(''.round($2).'')", $tag ); //get the rounded font size       
		$tag = preg_replace($regex3, "('')", $tag ); //remove the inline font-size style
		$tag = preg_replace($regex4, "('$1tag-size-'.($size).' $2$3')", $tag ); //add .tag-size-{nr} class
		$tagn[] = $tag;
	}     
	$taglinks = implode('</a>', $tagn);     
return $taglinks; 
}

For the code, also see the pastebin.

The added css classes can for instance be used to color the tags according to the number of appearance; as you can see here in the tag cloud when you scroll down on the left.