library(openxlsx)
library(dplyr)

df<-read.xlsx("http://kanggc.iptime.org/book/data/subtotal-e.xlsx")
df

summary(df)
summarise(df,mean_mid=mean(mid),mean_final=mean(final),mean_total=mean(total))
summarise(df,sd_mid=sd(mid),sd_final=sd(final),sd_total=sd(total))

class <- df %>% 
  group_by(class) %>%
  summarise(mean_mid = mean(mid),
  mean_final = mean(final),          
  mean_total = mean(total))
class

dept<-df%>%
  group_by(dept)%>%
  summarise(mean_mid=mean(mid),
            mean_final=mean(final),
            mean_total=mean(total))
dept