How to combine mutate when the condition is the same but output is different?-CodePudding

For my data frame, in the column Unit, if "mg" is found, it is replaced with "g" and then the corresponding value in the column "Mass" is divided by 1000. I used mutate twice to achieve this. Is there any ways to combine the two mutate into one?

df %>% mutate(unit = case_when(unit == "mg" ~ "g"))
df %>% mutate(mass = case_when(unit == "mg" ~ mass / 1000))

CodePudding user response：

Create the logical condition as a column and reuse. As the replacement values are different, it is better to have it separately. Also, case_when by default changes the rest of the elements to NA. If the OP meant to keep the rest of the values from the original column, specify the TRUE ~ condition

library(dplyr)
df <- df %>%
   mutate(i1 = unit == 'mg', 
      unit = case_when(i1 ~ 'g', TRUE ~ unit), 
      mass = case_when(i1~ mass/1000, TRUE ~ mass), i1 = NULL)

CodePudding user response：

We can include several transformations (in this case the two transformations) inside the same mutate call, with a reversed order. If your case_when statement is that simple, ifelse is enought:

library(dplyr)

df %>% mutate(mass = ifelse(unit == 'mg', mass / 1000, mass), 
              unit = ifelse(unit == 'mg', 'g', unit))