case_when in mutate pipe

Question

It seems dplyr::case_when doesn't behave as other commands in a dplyr::mutate call. For instance:

library(dplyr)  case_when(mtcars$carb <= 2 ~ "low",           mtcars$carb > 2 ~ "high") %>%    table 

works:

. high  low    15   17  

But put case_when in a mutate chain:

mtcars %>%    mutate(cg = case_when(carb <= 2 ~ "low",                         carb > 2 ~ "high")) 

and you get:

 Error: object 'carb' not found 

while this works fine

mtcars %>%    mutate(cg = carb %>%             cut(c(0, 2, 8))) 

Answer 1

As of version 0.7.0 of dplyr, case_when works within mutate as follows:

library(dplyr) # >= 0.7.0 mtcars %>%    mutate(cg = case_when(carb <= 2 ~ "low",                         carb > 2  ~ "high")) 

For more information: http://dplyr.tidyverse.org/reference/case_when.html

Answer 2

We can use .$

mtcars %>%        mutate(cg = case_when(.$carb <= 2 ~ "low",  .$carb > 2 ~ "high")) %>%     .$cg %>%     table() # high  low  #  15   17