[R] eval parent.frame() twice

[Rune Schjellerup Philosof]

Peter Dalgaard skrev:
> Rune Schjellerup Philosof wrote:
>   
>> Hi
>>
>> I want to use a function (update) that in its body uses
>> eval(call, parent.frame())
>>
>> I would like to use this function in a function that does not contain
>> the variables referred to in 'call'. Those variables are instead in the
>> parent.frame() of my function (named 'second' below)
>>
>> Like this:
>> a <- 2
>>
>> evalu <- function(obj) {
>>  call <- obj$call
>>  eval(call, parent.frame())
>> }
>> first <- function() {
>>  a <- 3
>>  obj <- list(call=expression(a))
>>  second(obj)
>> }
>> second <- function(obj) {
>>  eval(evalu(obj), parent.frame())
>> }
>>
>> first() #returns 2, but I want 3.
>>
>>
>> How do I change 'second' such that the value of 'a' from 'first' is
>> returned?
>>
>>     
>
> You could use the "n" argument to parent.frame (or eval.parent) inside
> "evalu" and go two generations back instead of one. Somewhat neater, you
> could pass the desired environment directly to evalu, as in
>
> e <- parent.frame()
> evalu(obj, e)
>
> (I'm not sure it is actually needed to separate out the calculation of
> "e", but I tend to be paranoid about evaluating parent.frame() in
> function arguments.)
>
>
>   

Thanks for the answer, but it isn't what I need.
'evalu' is a replacement for a function that I cannot change
(update.default).
My question is: How do I accomplish this by only changing 'second'?

-- 
Med venlig hilsen
Rune Schjellerup Philosof
Ph.d.-studerende, Statistik, IST, SDU

Telefon:  6550 3607
E-mail:   rphilosof at health.sdu.dk
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