Thank you for the report.
Yes, a slight inconsistency, but not a bug, really.
>>>>> "JonS" == JonS <JonS@swintons.net>
>>>>> on Wed, 21 Jan 2004 17:36:40 +0100 (CET) writes:
JonS> Attempting to substitute a NA causes an
JonS> error in sub.
>> sub(x=NA,pattern="x",replacement="y")
JonS> Error in sub(pattern, replacement, x,
JonS> ignore.case, extended) : invalid argument
>> sub(x=NA,pattern=NA,replacement="y")
JonS> [1] NA
but the point is that NA's are not equal:
A simple 'NA' is logical, so one could argue
t should give an error in any case.
First note the following:
> str(sub(x=NA,pattern=NA, replacement="y"))
chr NA> str(cNA <- as.character(NA))
chr NA> str(sub(x=cNA,pattern=cNA, replacement="y"))
chr NA> str(sub(x=cNA,pattern="x", replacement="y"))
chr NA
So sub() works fine for character NA's .
JonS> The help page for sub says only For
JonS> 'regexpr' it is an error for 'pattern' to be
JonS> 'NA', otherwise 'NA' is permitted and
JonS> matches only itself. so that this behaviour
JonS> is undocumented.
JonS> I believe that sub(x=NA,pattern,replacement)
JonS> should always be NA.
We could extend sub() / gsub() to coerce its `x' to character,
then this would work,
or we should make it give an error because NA is logical, not a
character.
The first option would be inline with already allowing logical
NA for `pattern' in sub/gsub.
Opinions?