No problem:

        my %category_count;
        my %seen;
        
        sub handle_article {
            my ($path, $category, $article_body) = @_;
            ...
            # lots of stuff
            ...
        
            # count number of articles in each category
            if ( not $seen{ $path } ) {
              $category_count{ $category }++;
              $seen{ $path } = 1;
            }
        }

It's a bloody miracle, that's what it is.