else clause in map_if

[GuiMarthe]

I fell that i order for the map_if function to be really useful should have the possibility of calling an "else" function if the outcome of .predicate is false.

By default it should leave the object iterated alone, and not return anything.

[lionel-]

I don't think that will happen because ... can only be forwarded in one function. To deal with this I usually do it that way:

cnd <- map_lgl(x, predicate)
x <- map_if(x, cnd, fun1)
x <- map_if(x, !cnd, fun2)

[GuiMarthe]

Yes yes that is a possible solution. But it would be more concise if one could do it in one line, like>
x <- map_if(x, cnd, fun1, fun2)
Also, it makes sense since it sort of resembles ifelse and if_else

[lionel-]

in purrr's syntax, fun2 is passed to fun1 in your example.

[hadley]

We could have map_if_else(.x, .cnd, .true, .false, ...)

[lionel-]

without the dots?

[hadley]

We could still have dots, but they'd be passed to both .true and .false so they wouldn't be that useful. Should probably have .na too, for completeness.

[Athospd]

Why the following solution is not viable?

map_if_else <- function (.x, .p, .true, .false, .na = identity, ...) {
  
  sel <- purrr:::probe(.x, .p)
  out <- list_along(.x)
  out[which(sel)] <- map(.x[which(sel)], .true, ...)
  out[which(!sel)] <- map(.x[which(!sel)], .false, ...)
  out[is.na(sel)] <- map(.x[is.na(sel)], .na, ...)
  
  set_names(out, names(.x))
}

regards