library(dplyr)

name<-c("±è±âÈÆ","¹Ú¼öµ¿","¿ø¼±Èñ","À§°è¿µ","ÃÖµ¿ÆÈ","ÃÖÁ¾¿­","ÃÖÁ¾¼ö","±è±âÆÈ","ÀÌ»ó¼ö","°­Ã¢¼ö")
prin<-c(98,100,50,50,80,90,30,80,65,95)
micro<-c(82,92,45,100,95,60,30,25,70,90)
macro<-c(95,80,75,100,95,60,30,25,70,90)
df<-data.frame(name,prin,micro,macro)

df$sum<-df$prin+df$micro+df$macro
df$mean<-df$sum/3
df$PF<-ifelse(df$mean >= 60, "pass","fail")
df$grade<-ifelse(df$mean >= 90, "A", ifelse(df$mean >= 80, "B", ifelse(df$mean >= 70, "C", ifelse(df$mean >= 60, "D", "F"))))

select(df, prin, micro)
select(df, prin:macro)
select(df, -micro)
select(df, ends_with("cro"))
rename(df, À̸§=name, °æÁ¦¿ø·Ð=prin, ¹Ì½Ã°æÁ¦=micro, °Å½Ã°æÁ¦=macro, ÃÑÁ¡=sum, Æò±Õ=mean, À̼ö=PF, ÇÐÁ¡=grade)


df[order(df$mean,decreasing=T),]
df %>% arrange(desc(mean))

df[order(df$prin),]
df %>% arrange(prin)