R help - Nov 2006 - Can I execute the content of a character vector?

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On Mon, 13 Nov 2006, Luiz Rodrigo Tozzi wrote:
> Hi
> 
> I want to know if there is any possibility of "executing" the
content of a
> vector, for example:
> 
> example=c("Test",1,0,0,0,"seq(14,42,by=2)",0,0,1)
> 
> i want to know if there is anything like "execute(example[6])"
You can say:

eval(parse(text=example[6]))

but it is difficult to avoid shooting people in the feet with it, unless 
that is what you want ...

eval(parse(text=example[1]))

> 
> i really need this because this object example is created from a parameter
> file with names, flags and this "seq" somethimes will be
something like
> c("1","99,"3") or even c("")
> 
> executing the content would be an easier step for me
> 
> thanks!
> 
> 
-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no

On 11/13/06, Roger Bivand <Roger.Bivand at nhh.no>
wrote:
> On Mon, 13 Nov 2006, Luiz Rodrigo Tozzi wrote:
>
> > Hi
> >
> > I want to know if there is any possibility of "executing"
the content of a
> > vector, for example:
> >
> > example=c("Test",1,0,0,0,"seq(14,42,by=2)",0,0,1)
> >
> > i want to know if there is anything like
"execute(example[6])"
>
> You can say:
>
> eval(parse(text=example[6]))
>
> but it is difficult to avoid shooting people in the feet with it, unless
> that is what you want ...
>
> eval(parse(text=example[1]))

We could enclose strings to be evaluated in backticks:

example <- c("Test",1,0,0,0,"`seq(14,42,by=2)`",0,0,1)

pat <- "^`(.*)`$"
f <- function(x)  # strip backticks in 1st and last posn and evaluate
   if (regexpr(pat, x) > 0)
      eval.parent(parse(text = sub(pat, "\\1", x)))
   else x

example <- c("Test",1,0,0,0,"`seq(14,42,by=2)`",0,0,1)
lapply(example, f)
>
>
> >
> > i really need this because this object example is created from a
parameter
> > file with names, flags and this "seq" somethimes will be
something like
> > c("1","99,"3") or even c("")
> >
> > executing the content would be an easier step for me
> >
> > thanks!
> >
> >
>
> --
> Roger Bivand
> Economic Geography Section, Department of Economics, Norwegian School of
> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
>
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