R devel - Jun 2011 - Syntactically valid names

Hi all,

Is there any easy way to tell if a string is a syntactically valid name?

e.g.

is.syntactic("X123")
# TRUE
is.syntactic("[[")
# FALSE

One implementation would be:

is.syntactic <- function(x) x == make.names(x)

but I wonder if there's a more elegant way.

Thanks!

Hadley

-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/

On Jun 30, 2011, at 22:37 , Hadley Wickham wrote:
> Hi all,
> 
> Is there any easy way to tell if a string is a syntactically valid name?
> 
> e.g.
> 
> is.syntactic("X123")
> # TRUE
> is.syntactic("[[")
> # FALSE
> 
> One implementation would be:
> 
> is.syntactic <- function(x) x == make.names(x)
> 
> but I wonder if there's a more elegant way.
I wouldn't expect so. The basic structure might be handled using a regexp of
sorts, but even that is tricky because of the "dot not followed by
number" rule, and then there's the stop list of reserved words, which
would make your code clumsy whatever you do.

How on Earth would you expect anything to be significantly more elegant than
your

function(x) x == make.names(x) 

anyway??! (OK, if there was a wrapper for the C level isValidName() function...)

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

On June 30, 2011 01:37:57 PM Hadley Wickham wrote:
> Is there any easy way to tell if a string is a syntactically valid name?
[...]
> 
> One implementation would be:
> 
> is.syntactic <- function(x) x == make.names(x)
> 
> but I wonder if there's a more elegant way.
This is without quoting, right? Because "make.names" replaces spaces
with
periods, and using quoting I can create syntactically valid names that do 
include spaces:

    `x prime` <- 3
    ls()

Davor