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Update transform_solutions.Rmd #4

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17 changes: 2 additions & 15 deletions transform_solutions.Rmd
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Expand Up @@ -96,21 +96,8 @@ arrange(flights, dep_delay)

### 3. Sort flights to find the fastest flights.
```{r}
# Note - this is a bit tricky since the time stamps are just encoded as integers
# so if a flight left at midnight (i.e. dep_time=2400) and arrived at 00:54 (arr_time=54),
# it's hard to just do arr_time - dep_time to get the travel time (you get back -2346, which doesn't make sense).
# Taking absolute values doesn't help either.
# A workaround solution is just to add 2400 if the travel time is ever negative.
# A better solution is to properly encode the times as timestamps
# note: we use the `mutate` function and the pipe character `%>%`, which haven't been introduced yet

flights %>% mutate(travel_time = ifelse((arr_time - dep_time < 0),
2400+(arr_time - dep_time),
arr_time - dep_time)) %>%
arrange(travel_time) %>% select(arr_time, dep_time, travel_time)

# for demonstration purposes, the naive solution is
arrange(flights, (arr_time - dep_time))
# use the variable air_time, which gives amount of time spent in the air, in minutes.
arrange(flights, air_time)

```

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