Automatic Classifying Self-Admitted Technical Debt Using N-Gram IDF. - Supatsara Wattanakriengkrai; Napat Srisermphoak; Sahawat Sintoplertchaikul; Morakot Choetkiertikul; Chaiyong Ragkhitwetsagul; Thanwadee Sunetnanta; Hideaki Hata; Kenichi Matsumoto (APSEC, 2019)