Count flights

How many flights departed in New York City in 2013?

flights %>% 
  count()

► Solution:

flights %>% 
  count()
## # A tibble: 1 x 1
##        n
##    <int>
## 1 336776

This is different to nrow():

flights %>% 
  nrow()
## [1] 336776

Count flights per airline

How many flights did each airline fly out of New York City in 2013?

flights %>% 
  count(___)

► Solution:

flights %>% 
  count(carrier)
## # A tibble: 16 x 2
##    carrier     n
##    <chr>   <int>
##  1 9E      18460
##  2 AA      32729
##  3 AS        714
##  4 B6      54635
##  5 DL      48110
##  6 EV      54173
##  7 F9        685
##  8 FL       3260
##  9 HA        342
## 10 MQ      26397
## 11 OO         32
## 12 UA      58665
## 13 US      20536
## 14 VX       5162
## 15 WN      12275
## 16 YV        601

Sum up distance per airline

What’s the total distance flown for all flights originating in New York City in 2013, per airline?

flights %>% 
  count(___, _____)

► Solution:

flights %>% 
  count(carrier, wt = distance)
## # A tibble: 16 x 2
##    carrier        n
##    <chr>      <dbl>
##  1 9E       9788152
##  2 AA      43864584
##  3 AS       1715028
##  4 B6      58384137
##  5 DL      59507317
##  6 EV      30498951
##  7 F9       1109700
##  8 FL       2167344
##  9 HA       1704186
## 10 MQ      15033955
## 11 OO         16026
## 12 UA      89705524
## 13 US      11365778
## 14 VX      12902327
## 15 WN      12229203
## 16 YV        225395

Useful summary functions

Don’t forget na.rm = TRUE if needed!

Mean arrival and dep delay

Compute the mean arrival and departure delay overall, and per origin airport. What is the standard deviation of these variables? What is New York City’s busiest airport?

flights %>%
  summarize(
    mean(___, na.rm = ___),
    _____,
    _____,
    _____
  )

flights %>%
  group_by(___) %>%
  summarize(_______)

flights %>%
  count(___) %>%
  arrange(___)

► Solution:

flights %>%
  summarize(
    mean(arr_delay, na.rm = TRUE),
    mean(dep_delay, na.rm = TRUE),
    sd(arr_delay, na.rm = TRUE),
    sd(dep_delay, na.rm = TRUE)
  )
## # A tibble: 1 x 4
##   `mean(arr_delay, … `mean(dep_delay, … `sd(arr_delay, n… `sd(dep_delay, n…
##                <dbl>              <dbl>             <dbl>             <dbl>
## 1               6.90               12.6              44.6              40.2
flights %>%
  summarize_at(
    vars(arr_delay, dep_delay),
    list(~ mean(., na.rm = TRUE), ~ sd(., na.rm = TRUE))
  )
## # A tibble: 1 x 4
##   arr_delay_mean dep_delay_mean arr_delay_sd dep_delay_sd
##            <dbl>          <dbl>        <dbl>        <dbl>
## 1           6.90           12.6         44.6         40.2
flights %>%
  group_by(origin) %>%
  summarize(
    mean(arr_delay, na.rm = TRUE),
    mean(dep_delay, na.rm = TRUE)
  )
## # A tibble: 3 x 3
##   origin `mean(arr_delay, na.rm = TRUE)` `mean(dep_delay, na.rm = TRUE)`
##   <chr>                            <dbl>                           <dbl>
## 1 EWR                               9.11                            15.1
## 2 JFK                               5.55                            12.1
## 3 LGA                               5.78                            10.3
flights %>%
  count(origin) %>%
  arrange(desc(n))
## # A tibble: 3 x 2
##   origin      n
##   <chr>   <int>
## 1 EWR    120835
## 2 JFK    111279
## 3 LGA    104662
flights %>%
  count(origin, sort = TRUE)
## # A tibble: 3 x 2
##   origin      n
##   <chr>   <int>
## 1 EWR    120835
## 2 JFK    111279
## 3 LGA    104662

Air time by carrier

Which carriers had the longest accumulated air time, excluding cancelled flights?

total_airtime_by_carrier <-
  flights %>%
  group_by(___) %>%
  summarize(acc_air_time = sum(_____)) %>% 
  ungroup()

total_airtime_by_carrier

► Solution:

total_airtime_by_carrier <-
  flights %>% 
  group_by(carrier) %>% 
  summarize(acc_air_time = sum(air_time, na.rm = TRUE)) %>% 
  ungroup()

total_airtime_by_carrier
## # A tibble: 16 x 2
##    carrier acc_air_time
##    <chr>          <dbl>
##  1 9E           1500801
##  2 AA           6032306
##  3 AS            230863
##  4 B6           8170975
##  5 DL           8277661
##  6 EV           4603614
##  7 F9            156357
##  8 FL            321132
##  9 HA            213096
## 10 MQ           2282880
## 11 OO              2421
## 12 UA          12237728
## 13 US           1756507
## 14 VX           1724104
## 15 WN           1780402
## 16 YV             35763

Air time by carrier, visualized

Plot a bar chart of the accumulated air time per airline, with a suitable unit for the total time.

Hint: Use fct_inorder() to fix the ordering of a categorical variable before plotting.

total_airtime_by_carrier <-
  _____
  
total_airtime_by_carrier %>%
  arrange(acc_air_time) %>%
  mutate(carrier = fct_inorder(carrier)) %>%
  ggplot(aes(___)) +
    geom_col()

► Solution:

total_airtime_by_carrier %>% 
  arrange(acc_air_time) %>%
  mutate(carrier = fct_inorder(carrier)) %>%
  ggplot() +
  geom_col(aes(carrier, acc_air_time / 60 / 24 / 365)) +
  coord_flip()

Carriers for long-distance routes

Which carriers specialize on long-distance routes?

mean_miles_by_carrier <-
  flights
  _____ %>%
  _____ %>%
  _____

mean_miles_by_carrier %>%
  arrange(_____)

► Solution:

mean_miles_by_carrier <-
  flights %>%
  group_by(carrier) %>% 
  summarize(mean_distance = mean(distance)) %>% 
  ungroup()

mean_miles_by_carrier %>%
  arrange(desc(mean_distance))
## # A tibble: 16 x 2
##    carrier mean_distance
##    <chr>           <dbl>
##  1 HA              4983 
##  2 VX              2499.
##  3 AS              2402 
##  4 F9              1620 
##  5 UA              1529.
##  6 AA              1340.
##  7 DL              1237.
##  8 B6              1069.
##  9 WN               996.
## 10 FL               665.
## 11 MQ               570.
## 12 EV               563.
## 13 US               553.
## 14 9E               530.
## 15 OO               501.
## 16 YV               375.

Mean distance, visualized

Plot a bar chart of mean distance per flight. Use fct_inorder() to avoid sorting the axes. Do you use geom_bar() or geom_col()? Why?

mean_miles_by_carrier <-
  _____ %>%
  _____ %>%
  _____

mean_miles_by_carrier %>%
  arrange(_____) %>%
  mutate(___ = fct_inorder(___)) %>%
  ggplot(aes(_____)) +
    geom____()

► Solution: We need geom_col(), because the data is already aggregated and contains one row per geometry object we’re plotting.

mean_miles_by_carrier <-
  flights %>%
  group_by(carrier) %>% 
  summarize(mean_distance = mean(distance)) %>% 
  ungroup()

mean_miles_by_carrier %>%
  arrange(desc(mean_distance)) %>%
  mutate(carrier = fct_inorder(carrier)) %>%
  ggplot() +
  geom_col(aes(x = carrier, y = mean_distance))

Worst plane

Which plane had the most failed departure attempts? Can you find a solution without filter()?

Hint: Use the idiom sum(___) to count the rows where a predicate is true.

flights %>%
  filter(is.na(dep_time)) %>%
  group_by(tailnum) %>%
  _____ %>%
  _____ %>%
  filter(!is.na(tailnum)) %>%
  arrange(desc(___)) %>% 
  head(1)

# Alternative without filter():
flights %>%
  group_by(tailnum) %>%
  _____ %>%
  _____ %>%
  arrange(_____) %>%
  head(1)

► Solution:

flights %>% 
  filter(is.na(dep_time)) %>%
  group_by(tailnum) %>% 
  summarize(not_departed = n()) %>% 
  ungroup() %>% 
  filter(!is.na(tailnum)) %>%
  arrange(desc(not_departed))
## # A tibble: 1,449 x 2
##    tailnum not_departed
##    <chr>          <int>
##  1 N725MQ            29
##  2 N713MQ            28
##  3 N723MQ            27
##  4 N15574            26
##  5 N722MQ            26
##  6 N13949            24
##  7 N14573            24
##  8 N735MQ            24
##  9 N11535            23
## 10 N11565            23
## # … with 1,439 more rows

Short-distance routes per airline, visualized

Compute the ratio of short-distance routes (less than 300 miles) for each airline.

Hint: Use the idiom mean(___) to compute the share of rows where a predicate is true.

flights %>%
  group_by(carrier) %>%
  _____ %>% 
  ungroup()

► Solution:

flights %>% 
  group_by(tailnum) %>% 
  summarize(not_departed = sum(is.na(dep_time))) %>% 
  ungroup()
## # A tibble: 4,044 x 2
##    tailnum not_departed
##    <chr>          <int>
##  1 <NA>            2512
##  2 D942DN             0
##  3 N0EGMQ            17
##  4 N10156             7
##  5 N102UW             0
##  6 N103US             0
##  7 N104UW             0
##  8 N10575            17
##  9 N105UW             0
## 10 N107US             0
## # … with 4,034 more rows

An alternative, using filter() and count():

flights %>% 
  filter(is.na(dep_time)) %>%
  count(tailnum, sort = TRUE)
## # A tibble: 1,450 x 2
##    tailnum     n
##    <chr>   <int>
##  1 <NA>     2512
##  2 N725MQ     29
##  3 N713MQ     28
##  4 N723MQ     27
##  5 N15574     26
##  6 N722MQ     26
##  7 N13949     24
##  8 N14573     24
##  9 N735MQ     24
## 10 N11535     23
## # … with 1,440 more rows

Short-distance routes per airline

Plot a bar chart of the ratio of short-distance routes.

short_distance_route_ratio <-
  _____

short_distance_route_ratio %>%
  ggplot(aes(___)) +
    geom_col()

► Solution:

short_distance_route_ratio <-
  flights %>%
  group_by(carrier) %>% 
  summarize(short_distance_ratio = mean(distance < 300)) %>% 
  ungroup() %>%
  arrange(desc(short_distance_ratio))

short_distance_route_ratio
## # A tibble: 16 x 2
##    carrier short_distance_ratio
##    <chr>                  <dbl>
##  1 YV                    0.531 
##  2 US                    0.469 
##  3 9E                    0.313 
##  4 EV                    0.288 
##  5 B6                    0.198 
##  6 MQ                    0.111 
##  7 UA                    0.0572
##  8 AA                    0.0445
##  9 OO                    0.0312
## 10 DL                    0.0252
## 11 WN                    0.0169
## 12 AS                    0     
## 13 F9                    0     
## 14 FL                    0     
## 15 HA                    0     
## 16 VX                    0
short_distance_route_ratio %>%
  ggplot() +
  geom_col(aes(x = fct_inorder(carrier), y = short_distance_ratio))

More exercises

Find more exercises in item 1 of Section 5.6.7 of r4ds.

Copyright © 2019 Kirill Müller. Licensed under CC BY-NC 4.0.