On Jul 6, 2011, at 03:25 , Hadley Wickham wrote:
>> What's wrong with that? They are names alright, just with special meanings.
>
> But you can't really use them for variables:
>
>> ... <- 4
>> ...
> Error: '...' used in an incorrect context
>> ..1 <- 4
>> ..1
> Error: 'nthcdr' needs a list to CDR down
>
> And make.names generally protects you against that:
>
>> make.names("function")
> [1] "function."
>> make.names("break")
> [1] "break."
>> make.names("TRUE")
> [1] "TRUE."
That's two different issues:
> y <- list()
> y$... <- 2
> y$..2 <- 3
> y$break <- 4
Error: unexpected 'break' in "y$break"
Notice that there is nothing _syntactically_ wrong with ... & friends as names:
> quote(...<-4)
... <- 4
It's the _evaluator_ that throws the error because the ...-name has a special
interpretation.
>
>>>> x <- paste(rep("x", 1e6), collapse = "")
>>>> x == make.names(x)
>>> [1] TRUE
>>
>> Mildly insane, but technically OK, no?
>
> I don't think so:
>
>> x <- paste(rep("x", 1e6), collapse = "")
>> assign(x, 1)
> Error in assign(x, 1) : variable names are limited to 10000 bytes
But that's a sanity check, with an arbitrary cutoff. A string of a million
"x"s is syntactically a valid name, it's just the evaluator that refuses to
play with it. (Not to say that it would be wrong to put in a similar sanity
check in make.names.)
--
Peter Dalgaard
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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