flights, dep_time %% 2400 <= 600)

There is one remaining issue. Midnight is represented by 2400, which would correspond to 1440 minutes since midnight, but it should correspond to 0. After converting all the times to minutes after midnight, x %% 1440 will convert 1440 to zero while keeping all the other times the same. Now we will put it all together. The following code creates a new data frame flights_times with columns dep_time_mins and sched_dep_time_mins. These columns convert dep_time and sched_dep_time, respectively, to minutes since midnight. flights_times <- mutate(flights, dep_time_mins = (dep_time %/% 100 * 60 + dep_time %% 100) %% 1440, sched_dep_time_mins = (sched_dep_time %/% 100 * 60 + sched_dep_time %% 100) %% 1440

arrange(flights, distance / air_time * 60)

c(600, 1200, 2400) %% 2400

filter(flights, between(month, 7, 9))

desc(is.na(dep_time)), dep_time)