Filter by vector values with for loop

November 19, 2021

Pretty new to this so…..Trying to count the number of flights that arrived at a certain location ahead of schedule in the nycflights13 dataset by carrier. Trying to do this using for loops. The steps below get me ONE result but I can’t seem to figure out the loop

#vectors for filtering
AL <- unique(flights$carrier)
LOC <- unique(flights$dest)

EARLYBIRD <- filter(flights, arr_delay < 0)

#want to repeat for "IAH" for all AL values, 
#placing each in STEP3 then move on to the 
#next value of LOC and so on.

STEP1 <- filter(EARLYBIRD, dest == "IAH")
STEP2 <- filter(STEP1, carrier == "UA")
STEP3 <- data.frame("IAH", "UA", nrow(STEP2))

I’d like to keep adding the last step to a data frame with dest, carrier, count.

Thanks for any help!

>Solution :

Don’t use for loops for this. This is what group_by is for.

EARLYBIRD %>%
  group_by(dest, carrier) %>%
  summarize(n = n())

Or, this use case is so common there is a specialty function count:

EARLYBIRD %>% count(dest, carrier)

The above will give you the counts for all destination/carrier combinations. If you don’t want all combinations, filter out the destinations or carriers you don’t want to see first.