[Rd] NA handling in as.character applied to a list

[Peter Dalgaard]

Seth Falcon <sfalcon at fhcrc.org> writes:

> Hi all,
> 
> In some circumstances, as.character applied to a list converts real
> NA's into the string "NA".  Propagation of NAs is something R does
> very well and unless there are good reasons for losing the NA, it
> would improve the consistency w.r.t. NA handling for as.character to
> behave differently.
> 
> Here's an example:
> 
> ## Create a list with character, logical, and integer NA elements
> v <- list(a=as.character(NA), b=NA, c=as.integer(NA))
> sapply(v, is.na)
> 
>        a    b    c 
>     TRUE TRUE TRUE 
> 
> sapply(as.character(v), is.na)
> 
>      <NA>    NA    NA 
>      TRUE FALSE FALSE 
> 
> Thoughts?

Hmm...

> as.character(v)
[1] NA   "NA" "NA"

This does look like a leftover from times when there was no character
NA in the language. It is the kind of thing you need to be very
careful about fixing though. (I have a couple of scars from
as.character on formulas when introducing backtick quoting.)


BTW, another little bit of nastiness popped up when playing around
with this:

> dput(v,control="all")
structure(list(a = NA, b = NA, c = as.integer(NA)), .Names = c("a",
"b", "c"))

> sapply(v,mode)
          a           b           c
"character"   "logical"   "numeric"



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