10.5 Transforming Variables with dplyr

In dplyr you transform variables with the function mutate(). Here is an example:

survey %>% 
  mutate(dareDevil = fastest > 125) %>%
  select(sex, fastest, dareDevil)

## # A tibble: 71 x 3
##    sex    fastest dareDevil
##    <fct>    <int> <lgl>    
##  1 male       119 FALSE    
##  2 male       110 FALSE    
##  3 female      85 FALSE    
##  4 female     100 FALSE    
##  5 male        95 FALSE    
##  6 male       100 FALSE    
##  7 male        85 FALSE    
##  8 male       160 TRUE     
##  9 female      90 FALSE    
## 10 female      90 FALSE    
## # … with 61 more rows

In mutate() there is always a variable-name on the left-hand side of the = sign. It could be the same as an existing variable in the table if you are content to overwrite that variable. On the right side of the = is a function that can depend on variables in the data table.

You can transform more than one variable in a single call to mutate(), as in the code below. The output is shown in 10.2.

survey %>% 
  mutate(dareDevil = fastest > 125,
         speedKmHr = fastest * 1.60934) %>% 
  ggplot(aes(x = dareDevil, y = GPA)) +
    geom_boxplot(fill = "burlywood", outlier.alpha = 0) +
    geom_jitter(width = 0.2)

Figure 10.2: Graph produced after mutation.

10.5.1 Practice Exercises

1. In mosaicData::CPS85 transform the wage variable to units of dollars per day. (Assume an 8-hour working day.)

10.5.2 Solutions to Practice Exercises

1. Try this:

   CPS85 %>% 
     as_tibble() %>%                   # for display in Console
     mutate(dailyWage = wage * 8) %>% 
     select(sex, sector, dailyWage)    # for display in Console

   ## # A tibble: 534 x 3
   ##    sex   sector   dailyWage
   ##    <fct> <fct>        <dbl>
   ##  1 M     const         72  
   ##  2 M     sales         44  
   ##  3 F     sales         30.4
   ##  4 F     clerical      84  
   ##  5 M     const        120  
   ##  6 F     clerical      72  
   ##  7 F     service       76.6
   ##  8 M     sales        120  
   ##  9 M     manuf         88  
   ## 10 F     sales         40  
   ## # … with 524 more rows