R help - Aug 2009 - how to pass user input to a function?

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

Hi Ista -

I've had success using the do.call function with RApache

 do.call(func, arglst)

where 'func' is the function you desire to use, 'arglst' is a
list of arguments.

You may need to do some cleanup of the arguments using evalq()
function (so that numbers are treated as numbers, for example).

HTH,

Mike
-- 
p: 415.860.4347
b: www.dataspora.com/blog
t: www.twitter.com/dataspora

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
>
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