WordPress: Set default category for a new post using links

set-default-post-category.php

function set_category () {

	global $post;
  //Check for a category parameter in our URL, and sanitize it as a string
	$category_slug = filter_input(INPUT_GET, 'category', FILTER_SANITIZE_STRING, array("options" => array("default" => 0)));
  
  //If we've got a category by that name, set the post terms for it
	if ( $category = get_category_by_slug($category_slug) ) {
		wp_set_post_terms( $post->ID, array($category->term_id), 'category' );
	}

}

//hook it into our post-new.php specific action hook
add_action( 'admin_head-post-new.php', 'set_category', 10, 1 );