1. School of Computer and Information Technology, Beijing Jiaotong University, Beijing 100044, China
2. Research Center on Fictitious Economy and Data Science, The Chinese Academy of Sciences, Beijing 100190, China
3. The Key Laboratory of Big Data Mining and Knowledge Management, Chinese Academy of Sciences, Beijing 100190, China
4. College of Information Science and Technology, University of Nebraska at Omaha, Omaha, NE 68182, USA