除了選擇現(xiàn)有的列，我們?cè)谟肦語(yǔ)言做數(shù)據(jù)分析時(shí)還時(shí)常需要添加新的列，心裂是現(xiàn)有列的函數(shù)，mutate的存在感很強(qiáng)！

mutate() 總是將新列添加在數(shù)據(jù)集的最后，因此我們需要先創(chuàng)建一個(gè)更狹窄的數(shù)據(jù)集，以

便能夠看到新變量。記住，當(dāng)使用 RStudio 時(shí)，查看所有列的最簡(jiǎn)單的方法就是使用 View()

函數(shù)：

flights_sml <- select(flights,
year:day,
ends_with("delay"),
distance,
air_time
)
mutate(flights_sml,
gain = arr_delay - dep_delay,
speed = distance / air_time * 60
)
#> # A tibble: 336,776 × 9
#> year month day dep_delay arr_delay distance air_time
#> <int> <int> <int> <dbl> <dbl> <dbl> <dbl>
#> 1 2013 1 1 2 11 1400 227
#> 2 2013 1 1 4 20 1416 227
#> 3 2013 1 1 2 33 1089 160
#> 4 2013 1 1 -1 -18 1576 183
#> 5 2013 1 1 -6 -25 762 116
#> 6 2013 1 1 -4 12 719 150
#> # ... with 3.368e+05 more rows, and 2 more variables:
#> # gain <dbl>, speed <dbl>

一旦創(chuàng)建，新列就可以立即使用：
mutate(flights_sml,
gain = arr_delay - dep_delay,
hours = air_time / 60,
gain_per_hour = gain / hours
)
#> # A tibble: 336,776 × 10
#> year month day dep_delay arr_delay distance air_time
#> <int> <int> <int> <dbl> <dbl> <dbl> <dbl>
#> 1 2013 1 1 2 11 1400 227
#> 2 2013 1 1 4 20 1416 227
#> 3 2013 1 1 2 33 1089 160
#> 4 2013 1 1 -1 -18 1576 183
#> 5 2013 1 1 -6 -25 762 116
#> 6 2013 1 1 -4 12 719 150
#> # ... with 3.368e+05 more rows, and 3 more variables:
#> # gain <dbl>, hours <dbl>, gain_per_hour <dbl>

如果只想保留新變量，可以使用transmute（）函數(shù)：

transmute(flights,
gain = arr_delay - dep_delay,
hours = air_time / 60,
gain_per_hour = gain / hours
)
#> # A tibble: 336,776 × 3
#> gain hours gain_per_hour
#> <dbl> <dbl> <dbl>
#> 1 9 3.78 2.38
#> 2 16 3.78 4.23
#> 3 31 2.67 11.62
#> 4 -17 3.05 -5.57
#> 5 -19 1.93 -9.83
#> 6 16 2.50 6.40
#> # ... with 3.368e+05 more rows