[R] a question about function eval()

[Feng Chen]

----- Original Message ----- 
From: "Feng Chen" <fengchen at hkusua.hku.hk>
To: "Uwe Ligges" <ligges at statistik.uni-dortmund.de>
Sent: Thursday, February 24, 2005 9:52 PM
Subject: Re: [R] a question about function eval()


> Dear Uwe,
>
> Thanks for your advice. As you may have noticed, I am a newbie to R and 
> not fully aware of the power of such mechanisms like eval(), call(), 
> substitute(), ...
>
> In fact, the likelihood function I want to maximize has a nonparametric 
> component. I am trying to approximate it using special functions of known 
> form but with a finite number, say n, of unknown parameters. I want the 
> number n to be variable, so I use vector formals to pass into the 
> (log)likelihood function the parameters of the approximating function. I 
> tried to maximize the loglikelihood, but without success. Then I guess the 
> function passed into mle() should not have vectors or lists as its 
> arguments. Therefore, I try to generate functions with a variable number 
> of arguments based on the loglikelihood function and use mle() to the new 
> functions. That is why I have got all these troubles. Maybe there are more 
> convenient alternatives I simply don't know.
>
> By the way, If I use objects globally visible (such as constants) as the 
> default values for coef.sex,...,knot.val.n. Then it does work. But now I 
> am just curious whether it is possible to use objects existing in the 
> parent function as the default values for the arguments of the child 
> function (in this eval() case).
>
> Any advice is appreciated,
> Feng
>
> ----- Original Message ----- 
> From: "Uwe Ligges" <ligges at statistik.uni-dortmund.de>
> To: "Feng Chen" <fengchen at hkusua.hku.hk>
> Cc: <r-help at stat.math.ethz.ch>
> Sent: Thursday, February 24, 2005 7:59 PM
> Subject: Re: [R] a question about function eval()
>
>
>> Feng Chen wrote:
>>
>>> Hi,
>>>
>>> I have a question about the usage of eval(). Wonder if any experienced 
>>> user can help me out of it.
>>>
>>> I use eval() in the following function:
>>> semireg.pwl <- 
>>> function(coef.s=rnorm(1),coef.a=rnorm(1),knots.pos=knots.x,knots.ini.val=knots.val){
>>>   knotn <- length(knots.pos)
>>>   def.par.env <- sys.frame(1)
>>>   print(def.par.env)
>>>   print(environment(coef.s))
>>>   tg <- eval( (parse(text=
>>>                      paste(
>>>                            "function(coef.sex=coef.s,coef.age=coef.a,",
>>>
>>> paste("knot.val.",1:knotn,"=knots.ini.val[",1:knotn,"]",sep="",collapse=","),
>>>                            ")",
>>>                            "{\n print(sys.frame());print(coef.sex)\n  y 
>>> <- c(",
>>>
>>> paste("knot.val.",1:knotn,sep="",collapse=","),
>>>                            ")\n",
>>>
>>> 
>>>                          "  -loglikelihood(coef.sex,coef.age,knots.pos,y)\n}",
>>>                            sep="",collapse=""
>>>                            )
>>>                      )
>>>                )
>>>              ,envir=def.par.env)
>>
>> Why do you want to use eval(parse(.....))? That's not sensible in this 
>> case. You can either alculate the stuff doirectly or define a function 
>> instead....
>>
>> Uwe Ligges
>>
>>
>>
>>>   print(tg())
>>>   print(coef.s)
>>>   print(sys.frame(1))
>>>   mle(tg)
>>> }
>>>
>>> But when I ran semireg.pwl(), I got correct value for tg(), but an 
>>> message "Error in eval(expr, envir, enclos) : Object "coef.s" not found" 
>>> for mle(tg). I just don't know how to make the environment variable 
>>> visible for mle().
>>>
>>> Thanks a lot!
>>>
>>> Feng
>>> [[alternative HTML version deleted]]
>>>
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>