> On 27 Apr 2015, at 13:48 , Hadley Wickham <h.wick...@gmail.com> wrote:
>
> Sometimes the absence of a name is maked by an NA:
>
> x <- 1:2
> names(x)[[1]] <- "a"
> names(x)
> # [1] "a" NA
>
> Whereas other times its
>
> y <- c(a = 1, 2)
> names(y)
> # [1] "a" ""
>
> Is this deliberate? The help for names() is a bit murky, but an
> example shows the NA behaviour.
I think it is
(a) impossible to change
(b) at least somewhat coherent
The situation is partially due to the fact that character-NA is a relative
latecomer to the language. In the beginning, there was no real distinction
between NA and "NA", causing issues when abbreviating Noradrenaline, North
America, Nelson Anderson, etc. At some point, it was decided to fix things up,
as far as possible in a backawards compatible way. Some common idioms were
retained but others were changed to comply with the rules for other vector
types.
We have the empty string convention on (AFAICT) all constructor usages:
c(a=1, 3)
list(a=1, 3)
cbind(a=1, 3)
and also in the lists implied by argument matching
> f <- function(...) names(match.call(expand.dots=TRUE))
> f(a=1,3)
[1] "" "a" ""
In contrast, assignment forms have the NA convention. This is consistent with
the general rules for complex assignment. E.g. we have
> a <- "a"
> a[[5]] <- "b"
> a
[1] "a" NA NA NA "b"
and even
> a <- NULL
> a[[5]] <- "a"
> a
[1] NA NA NA NA "a"
also, we have
> l <- list(1,2,3)
> names(l) <- c("a","b")
> l
$a
[1] 1
$b
[1] 2
$<NA>
[1] 3
and we do want to obey general rules like
names(l)[[2]] <- "a"
being (nearly) equivalent to
`*tmp*`<- names(l)
`*tmp*`[[2]] <- "a"
names(l) <- `*tmp*`
- pd
>
> Hadley
>
> --
> http://had.co.nz/
>
> ______________________________________________
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--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
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