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