Classification of patent classes into technological categories and sub-categories based on the last version of U.S. Patent Classification System and following the method described in Hall, Jaffe, and Trajtenberg (2001, NBER working paper no.8498). A technical note Wang (2020) "Patent Classification Systems and Technological Categorization: An Overview and Update" is available at https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3220033.
Caution note: in the uploaded file, I still kept US patent class no.1 for consistency (with the original version), although this class should be handled carefully depends on the research question. In general, it does not bring much information on the underlying technology, as the class title for class no.1 is "** Classification Undetermined **".