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
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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