pmap returns output length zero if at least one element is length 0

[benjaminschwetz]

Edit: related to #679

Regarding inputs of length 0, the documentation for pmap() / map2() states under values:

If all input is length 0, the output will be length 0.

I deducted from this statement that the output would not be length zero, if all inputs would not be 0. I.e. NULLs would be passed on to the functions together with the other elements. However, if I pass a list with at least one element of length 0, to pmap(), the output is length 0.

l <- list(letters, LETTERS, NULL)
x <- purrr::pmap(l,c)
x
#> list()
#What I would expect x to look like:
list(
  c(letters[1], LETTERS[1], NULL),
  c(letters[2], LETTERS[2], NULL),
  c(letters[3], LETTERS[3], NULL)
  # etc.
)
#> [[1]]
#> [1] "a" "A"
#> 
#> [[2]]
#> [1] "b" "B"
#> 
#> [[3]]
#> [1] "c" "C"

^{Created on 2019-07-31 by the reprex package (v0.3.0)}

[lionel-]

In the future this will probably become an error. We have adopted the rule that only length 1 vectors can be recycled. See discussion in tidyverse/design#13

[hadley]

Now duplicate of #878