根据其他列的分组在R数据框中创建新列

Question

Using mtcars from the datasets package, I want to added an addition column that is created from mtcars$mpg , such that:

If mtcars$mpg >=15 and <19 then "Good"
If mtcars$mpg >=19 and <27 then "Average"
If mtcars$mpg >=27 then "Bad"

Answer 1

You can use ifelse()

mtcars$mpg2 <- ifelse(mtcars$mpg >=15 & mtcars$mpg < 19,
                      "Good",
                      ifelse(mtcars$mpg >=19 & mtcars$mpg < 27,
                             "Average",
                             ifelse(mtcars$mpg > 27, "Bad", "")))

Answer 2

If you want the tidyverse solution, try this:

library(tidyverse)

df <- as_tibble(mtcars)

df %>% 
  mutate(mpg_quality = case_when(mpg >= 15 & mpg < 19 ~ "good",
                                 mpg >= 19 & mpg < 27 ~ "average",
                                 mpg >= 27 ~ "bad"))

Which gives us:

# A tibble: 32 x 12
     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb mpg_quality
   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>       <chr>
 1  21.0     6 160.0   110  3.90 2.620 16.46     0     1     4     4     average
 2  21.0     6 160.0   110  3.90 2.875 17.02     0     1     4     4     average
 3  22.8     4 108.0    93  3.85 2.320 18.61     1     1     4     1     average
 4  21.4     6 258.0   110  3.08 3.215 19.44     1     0     3     1     average
 5  18.7     8 360.0   175  3.15 3.440 17.02     0     0     3     2        good
 6  18.1     6 225.0   105  2.76 3.460 20.22     1     0     3     1        good
 7  14.3     8 360.0   245  3.21 3.570 15.84     0     0     3     4        <NA>
 8  24.4     4 146.7    62  3.69 3.190 20.00     1     0     4     2     average
 9  22.8     4 140.8    95  3.92 3.150 22.90     1     0     4     2     average
10  19.2     6 167.6   123  3.92 3.440 18.30     1     0     4     4     average
# ... with 22 more rows

The df <- as_tibble(mtcars) isn't necessary but I like tibbles so I included it.