数据示意如下:
- * Example generated by -dataex-. To install: ssc install dataex
- clear
- input long id int year byte a
- 201100006 2015 1
- 201100006 2017 0
- 201100007 2015 1
- 201100007 2017 1
- 201100008 2015 0
- 201100008 2017 0
- 201100013 2015 0
- 201100013 2017 0
- 201100016 2015 0
- 201100016 2017 1
- end