NA handling in as.character applied to a list

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"

O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

Peter Dalgaard <p.dalgaard at biostat.ku.dk> writes:

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.)

Well, I guess that's an argument for leaving the inconsistent
behavior.  In case there is interest in fixing, here is a patch I was
playing with.  It doesn't address the nasties with dput.  


index 8eec5c3..787c230 100644
--- a/src/main/coerce.c
+++ b/src/main/coerce.c
@@ -1041,6 +1041,14 @@ #if 0
            else if (isSymbol(VECTOR_ELT(v, i)))
                SET_STRING_ELT(rval, i, PRINTNAME(VECTOR_ELT(v, i)));
 #endif
+            else if ((length(VECTOR_ELT(v, i)) == 1) && 
+                      (isInteger(VECTOR_ELT(v, i)) ||
+                       isReal(VECTOR_ELT(v, i)) ||
+                       isLogical(VECTOR_ELT(v, i)))) {
+                SET_STRING_ELT(rval, i, 
+                               STRING_ELT(coerceVector(VECTOR_ELT(v, i), 
+                                                       STRSXP), 0));
+            }
            else
                SET_STRING_ELT(rval, i,
                               STRING_ELT(deparse1line(VECTOR_ELT(v, i), 0), 0));