[R] How to read in expressions as function parameters?

[Alexwang]

Thanks a lot!




Henrique Dallazuanna wrote:
> 
> Try this:
> 
> form<- scan(file = "", what = character(0), n=1,strip.white =
>  TRUE,quiet=TRUE )
> form2<-parse(text=form)
> foo <- function(x){}
> body(foo) <- form2
> curve(foo,10,100)
> 
> On 09/12/2007, Alex Wang <alecwang80 at gmail.com> wrote:
>> Hi:
>>
>>    There, I've got a question about how to read in expressions as
>> function
>> parameters and it really bothered me.
>>
>>  I'm going to use curve() function to plot curves, and I'd like to write
>> a
>> menu function to let use input math expressions.
>>
>>   say, if I'd like curve(3*x*x-4/x, 10, 100), I use scan() to  read in
>> the
>> math expression
>>
>> form<- scan(file = "", what = character(0), n=1,strip.white =
>> TRUE,quiet=TRUE )
>> then get form as a string. "3*x*x-4/x"
>> Use parse() to convert it into expression
>> form2<-parse(text=form)
>> then form2=expression(3*x*x-4/x).
>>
>> However, curve(form2,10,100) doesn't work at all.
>>
>> Is there anyway to get this done?
>>
>> Thanks a lot!
>>
>> Alex
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> 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.
>>
> 
> 
> -- 
> Henrique Dallazuanna
> Curitiba-Paraná-Brasil
> 25° 25' 40" S 49° 16' 22" O
> 
> ______________________________________________
> 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.
> 
> 

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