use_first_valid_of leaves POSIX variables as numerics

[sfirke]

dat <- data.frame(a = c(as.POSIXct(as.Date("2006-12-12")), as.POSIXct(as.Date("2005-01-05"))))
dat$b <- dat$a + 1
use_first_valid_of(dat$a, dat$b)
[1] 1165881600 1104883200
Warning messages:
1: In if (class(vars[[1]]) == "factor") { :
  the condition has length > 1 and only the first element will be used
2: In if (class(vars[[1]]) == "Date") { :
  the condition has length > 1 and only the first element will be used

Right now it sets the result vector to class Date if inputs are Date which is insufficient. Can it just set to whatever the resulting class should be?

[sfirke]

That error message indicates a separate problem: some variables have multiple classes, like POSIXct and POSIXt, so saying class(x) == "factor" causes that error message above. Will also address that here by making the condition if(sum(class(vars[[1]]) %in% "factor") > 0).

[sfirke]

Turns out dplyr does not support POSIXlt variables.

[sfirke]

Ended up being a trickier fix than I thought. It didn't occur to me that POSIXlt is a list, not a vector, so it wasn't stored correctly in the nested for-loops and I was getting the not-helpful message $ operator is invalid for atomic vectors. Good thing I wrote POSIXlt unit tests when I wrote the POSIXct ones that covered my immediate problem :)