Working in r-devel, we're not allowed to use a list component name of
"":
> list(a = 1, "" = 2)
Error: attempt to use zero-length variable name
However, that's what gets reported to us if we create a list with no
name:
> x <- list(a = 1, 2)
> names(x)
[1] "a" ""
The names<- function apparently doesn't check for the error:
> x <- list(1, 2)
> names(x) <- c("a", "")
> names(x)
[1] "a" ""
and it allows all names to be blank:
> names(x) <- c("", "")
> names(x)
[1] "" ""
However, if we do it with a piece of language, things are different:
> x <- quote(list(1,2))
> x
list(1, 2)
> mode(x)
[1] "call"
> names(x)
NULL
> names(x) <- c("", "a", "")
> x
list(a = 1, 2)
> names(x) <- c("", "", "")
> x
list(1, 2)
> names(x)
NULL
I think the behaviour should be consistent between lists and call
objects; if the behaviour for calls followed the behaviour for lists,
it would let me save a line (if (is.null(names(x)) .... ) in the
margins function.
Even though they print the same way, names of c("", "", "") are
different from no names at all.
Duncan Murdoch
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