[R] Converting character to function argument

[Uwe Ligges]

Henrik Bengtsson wrote:

> eval() and parse() are you friends here. Possibly also substitute().
> Example:
> 
>  eval(parse(text="expand.grid(c(1,0),c(1,0))"))
> 
> However, I would like to reply with a question to you. Why do you end up
> with a string that you need to convert in the first place? 

That's the question, indeed!


 > Maybe you are
> more interested in a solution like the following one:
> 
> N <- 2
> l <- lapply(1:N, FUN=function(x) c(0,1))
> expand.grid(l)
 >
> Henrik Bengtsson
> Lund University



Or, if you are really going to work completely on characters (hence you 
have to be more specific!):

  do.call("expand.grid", rep(list(eval(parse(text = "c(1, 0)"))), 2))

Uwe Ligges


> 
>>-----Original Message-----
>>From: r-help-bounces at stat.math.ethz.ch 
>>[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
>>Alvaro.Antonio.Novo at bportugal.pt
>>Sent: den 12 september 2003 18:55
>>To: r-help at stat.math.ethz.ch
>>Subject: [R] Converting character to function argument
>>
>>
>>How can one transform a character string into an argument of 
>>a function (which is not or I don't want it to be a character string)?
>>
>>Example:
>>
>>
>>>expand.grid(c(1,0),c(1,0)) ## OK
>>
>>  Var1 Var2
>>1    1    1
>>2    0    1
>>3    1    0
>>4    0    0
>>
>>
>>
>>>paste(rep("c(0,1)",2),collapse=',') ## to be used below
>>
>>[1] "c(0,1),c(0,1)"
>>
>>>## string is the input I want, but it needs to be coerced to the 
>>>correct
>>
>>format
>>
>>
>>>expand.grid(paste(rep("c(0,1)",2),collapse=',')) ## does not get me 
>>>there
>>
>>           Var1
>>1 c(0,1),c(0,1)
>>