use 0624b\1,clear collapse (mean) gpa , by(year) list use https://www.stata-press.com/data/r16/college,clear collapse (mean) mean_gpa=gpa, by(year) list use https://www.stata-press.com/data/r16/college,clear collapse (mean) gpa hour, by(year) list *使用collapse分组计算统计量 *collapse能够将变量数据按照对应组别转换为多种统计量 h collapse sysuse auto,clear *根据维修次数(rep78)计算price的平均值 collapse (mean) price, by (rep78) ★说明:原始数据会丧失 sysuse auto,clear *根据维修次数(rep78）计算price的平均值,并将新变量命名为pricemean collapse (mean) pricemean=price, by (rep78) sysuse auto,clear ★可以同时计算多个变量和多个统计量 collapse (count) n=price (mean) price mpg, by(rep78) l *如何判断两列数据是否相同 sysuse auto,clear egen a = diff (price mpg) browse a price mpg