install.packages("hflights")
install.packages("dplyr")
library(hflights)
library(dplyr)

str(hflights)

colnames(hflights)
hflight_df = tbl_df(hflights)
hflight_df

# gain이라는 컬럼명의 ArrDelay - DepDelay 값의 파생변수 생성
aa = mutate(hflight_df, gain=ArrDelay-DepDelay)
aa