[R] how to pass user input to a function?

[Don MacQueen]

And an alternative to nested if else's, in a case where they are 
actually needed, is

     switch

-Don

At 1:06 PM -0400 8/25/09, Ista Zahn wrote:
>Nice one Gabor! It works great, and is really simple. Bill Dunlap's 
>solution of
>
>GET$pass.var <- as.name(GET$pass.var)
>eval(substitute(mean(x), list(x=GET$pass.var)))
>
>also works.
>
>Thanks!
>
>
>On Tue, Aug 25, 2009 at 12:59 PM, Gabor
>Grothendieck<ggrothendieck at gmail.com> wrote:
>>  Try this:
>>
>>  x <- get(GET$pass.var)
>>  mean(x)
>>
>>
>>  On Tue, Aug 25, 2009 at 12:26 PM, Ista 
>>Zahn<izahn at psych.rochester.edu> wrote:
>>>  Hi everyone,
>>>  I'm building a website (http://*yourpsyche.org) using  Jeffrey Horner's
>>>  awesome Rapache module. I want to take user input, and pass it to an R
>>>  script. At first I was simply using if else statements, but after a
>>>  while I had so many nested if else's in my code that my head was
>>>  spinning. So then I started using cat() and source() to write
>>>  temporary files and read them back in (see example below). I've
>>>  searched around, and I think there might be a better way to do it with
>>>  substitute(), but I can't seem to figure it out (see attempt below).
>>>
>>>   Here is a minimal example:
>>>
>>>>  ###set up simple example###
>>>>  GET <- list(pass.var="b")
>>>>  a <- 1:10
>>>>  b <- 11:20
>>>>
>>>>  ###using if else works but becomes confusing when I have a lot 
>>>>of variables to pass###
>>>>  if(GET$pass.var=="a")
>>>  +   {
>>>  +     mean(a)
>>>  +   } else if(GET$pass.var=="b")
>>>  +   {
>>>  +     mean(b)
>>>  +   }
>>>  [1] 15.5
>>>>
>>>>  ###writing to a temporary file works but feels like a hack and 
>>>>results in many temp
>  >> files###
>  >>> cat('print(mean(', GET$pass.var,'))', file="tmp.R",sep="")
>  >>> source("tmp.R")
>  >> [1] 15.5
>  >>>
>  >>> ###this seems promising but I can't figure it out###
>  >>> substitute(mean(x), list(x=GET$pass.var))
>>>  mean("b")
>>>>
>>>>  ###is there a better way?###
>>>>
>>>
>>>  Thanks!
>>>  --
>>>  Ista Zahn
>>>  Graduate student
>>>  University of Rochester
>>>
>>>  ______________________________________________
>>>  R-help at r-project.org mailing list
>>>  https://*stat.ethz.ch/mailman/listinfo/r-help
>>>  PLEASE do read the posting guide 
>>>http://*www.*R-project.org/posting-guide.html
>>>  and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>
>
>
>--
>Ista Zahn
>Graduate student
>University of Rochester
>
>______________________________________________
>R-help at r-project.org mailing list
>https://*stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide http://*www.*R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.


-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062