Wordpress. Exclude post category from homepage or blog

gistfile1.txt

//Remember the ID number of the category (in this case, the number is 55)
//Open functions.php file from the active theme
//Copy and paste the code and replace “xx” with the category ID (leave the minus sign in the code)


function exclude_category($query) {
if ( $query->is_home() ) {// set this to "is_archive()" to remove from blog
$query->set( 'cat', '-xx' );
}
return $query;
}
add_filter( 'pre_get_posts', 'exclude_category' );