mutate two or more columns if case_when is used

Question

I am trying to use the case_when function for a bunch of columns y a data.frame.

This case does not return the specified columns in mutate

Answer 1

Discover this solution, but is a bit weird and tricky

mutate_when <- function (data, ...) {
  dots <- eval (substitute (alist(...)))
  for (i in seq (1, length (dots), by = 3)) {
    condition <- eval (dots [[i]], envir = data)
    mutations <- eval (dots [[i + 1]], envir = data [condition, ])
    data[condition, names(mutations)] <- mutations
    mutations_else <- eval (dots [[i + 2]], envir = data [!condition, ])
    data[!condition, names(mutations)] <- mutations_else
  }
  data
}

cars %>%
  mutate(
    km = speed * dist, 
    mt = km/1000
  ) %>%
  mutate_when(
    speed < 20, 
    list (
      km = km * 2,
      mt = mt * 3
    ),
    list (
      0
    )
  )

Gives

   speed dist   km    mt
1      4    2   16 0.024
2      4   10   80 0.120
3      7    4   56 0.084
4      7   22  308 0.462
5      8   16  256 0.384
6      9   10  180 0.270

Answer 2

We could use mutate_at

library(tidyverse)
cars %>%
   mutate(km = speed * dist, mt = km/1000) %>%
   mutate_at(vars(km, mt), funs(case_when(speed < 20 ~ .*2,
                                      TRUE ~ .)))

---

If we need to do computation with separate values for each of the column, then use map2 or pmap

out <- cars %>%
         mutate(km = speed * dist, mt = km/1000)  %>%  
         select(km, mt) %>%
         map2_df(., list(2, 3), ~ 
           case_when(cars$speed < 20 ~ .x * .y, TRUE ~ .x)) %>% 
         bind_cols(cars, .)

head(out)
#  speed dist  km    mt
#1     4    2  16 0.024
#2     4   10  80 0.120
#3     7    4  56 0.084
#4     7   22 308 0.462
#5     8   16 256 0.384
#6     9   10 180 0.270