On Fri, 7 Oct 2005, Duncan Murdoch wrote:
I haven't been following this conversation in order, but I think there's
another bug here besides the one(s?) you identified:
Jens had this example:
x <- 1:4
names(x) <- c(NA, "NA", "a", "")
x[names(x)]
<NA> <NA> a <NA>
1 1 3 NA
Shouldn't the second entry in the result be 2, with name "NA"? It seems the
string "NA" has been converted to <NA> here.
Yes, but I don't see it in PR#8161 where there is no name "NA" that I can
see. (In other words it is not an instance of the subject line.)
The issue is that <NA> is matching "NA", and it should not. As in the
code
Rboolean NonNullStringMatch(SEXP s, SEXP t)
{
if (CHAR(s)[0] && CHAR(t)[0] && strcmp(CHAR(s), CHAR(t)) == 0)
return TRUE;
else
return FALSE;
}
and there are more instances around.
Duncan Murdoch
Prof Brian Ripley wrote:
On Thu, 6 Oct 2005, "Jens Oehlschlägel" wrote:
Dear Thomas,
This looks deliberate (there is a function NonNullStringMatch that does
the matching). I assume this is because there is no other way to
indicate that an element has no name.
If so, it is a documentation bug -- help(names) and FAQ 7.14 should
specify this behaviour. Too late for 2.2.0, unfortunately.
I respectfully disagree: the element has a name, its an empty string. Of
course "" is a doubtful name for an element, but as long as we allow this
name when assigning names()<- we also should handle it like a name in
subscripting. The alternative would be to disallow "" in names at all.
However, both alternatives rather look like code changes, not only
documentation.
I think Thomas is right as to how S interprets this: "" is no name on
assignment, wheread NA as a name is a different thing (there probably is a
name, we just do not know what it is).
Here is the crux of the example.
p <- c(a=1, 2)
p <- c(a=1, 2)
names(p)
[1] "a" ""
p
a
1 2
p2 <- c(1,2)
names(p2) <- c("a", "")
identical(p, p2)
[1] TRUE
so giving the name is "" really is the same as giving no name.
`Error 1' is said to be
p[""]
<NA>
NA
You haven't given a name, so I think that is right. S (which has no
character NAs) uses "" as the name, but here there may be a name or not.
P <- list(a=1, 2)
I think Jens then meant as `error 2' that
P
$a
[1] 1
[[2]]
[1] 2
shows no name for the second element, and that seems right to me (although
S shows "" here).
Finally (`error 3')
P[""]
$"NA"
NULL
is a length-one list with name character-NA. (S has no name here.) That
seems the right answer but if so is printed inconsistently.
I would say that
Q <- list(1, 2)
names(Q) <- c("a", NA)
Q
$a
[1] 1
$"NA"
[1] 2
was the only bug here (the name should be printed as <NA>). Now that
comes from this bit of code
if( isValidName(CHAR(PRINTNAME(TAG(s)))) )
sprintf(ptag, "$%s", CHAR(PRINTNAME(TAG(s))));
else
sprintf(ptag, "$\"%s\"", CHAR(PRINTNAME(TAG(s))));
so non-syntactic names are printed surrounded by "". Nowadays I think we
would prefer ``, as in
A <- list("a+b"=1)
A
$"a+b"
[1] 1
A$"a+b"
[1] 1
A$`a+b`
[1] 1
but NA needs to be a special case as in
A <- list(1, 2)
names(A) <- c("NA", NA)
A
$"NA"
[1] 1
$"NA"
[1] 2
is.na(names(A))
[1] FALSE TRUE
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Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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