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.
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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