[R] Extracting Coefficients and Such from mle2 Output

[David Winsemius]

Let me  admit at this point that I am not really sure that S4 classes  
is the correct classification of such "@"-using extraction processes.  
The documentation refers to "formal methods" and I don't yet have  
enough knowledge to know that how tightly slots and formal classes are  
linked with S4 or S3.

-- 
David Winsemius

On Feb 1, 2009, at 10:43 AM, David Winsemius wrote:

>
> As Ben Bolker's reply hints, our difficulty was that because we were  
> insufficiently knowledgeable regarding working with S4 objects such  
> as  "a" and summary(a) object. Both mle2 and summary(a) produce S4  
> objects which need a different set of extraction technology.  
> Although I did not know it last night, I have now looked at the help  
> page for "slot", followed the link to the help page for "@" labeled  
> "slotOp",  and found that one can use "@" in much the same way one  
> uses "$".
>
> > str(summary(a))
> #Formal class 'summary.mle2' [package "bbmle"] with 3 slots
>  ..@ call  : language mle2(minuslogl = LL, fixed = list(xhalf = 6))
>  ..@ coef  : num [1, 1:4] 1.93e+01 1.71 1.13e+01 1.86e-29
>  .. ..- attr(*, "dimnames")=List of 2
>  .. .. ..$ : chr "ymax"
>  .. .. ..$ : chr [1:4] "Estimate" "Std. Error" "z value" "Pr(z)"
>  ..@ m2logL: num 60.4
>
> # So ....coef in this case is a 1 by 4 matrix and ...
>
> summary(a)@coef["ymax","Std. Error"]
>
> #yields
> #[1] 1.711541
>
> So we still have access to any of the components of an S4 object  
> such as a or summary(a), if we follow the trail of their respective  
> structures
> -- 
> David Winsemius
>
>
>
> On Feb 1, 2009, at 7:50 AM, BooBoo wrote:
>
>> I had asked this question once before about a function in the NADA  
>> package, and you provided this neat response:
>>
>> [Begin quote]
>>
>> An approach that may yield somewhat more self-documenting code  
>> would be to examine either the fit object or the summary object  
>> with str and then to access results by extracting named elements.  
>> Since I don't have the package in question, let me use the lm  
>> object on its help page as an example:
>>
>> ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
>> trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
>> group <- gl(2,10,20, labels=c("Ctl","Trt"))
>> weight <- c(ctl, trt)
>> lm.D9 <- lm(weight ~ group)
>>
>> str(lm.D9)
>> str(summary(lm.D9))
>> summary(lm.D9)$coefficients
>> summary(lm.D9)$coefficients["groupTrt", "Pr(>|t|)"]
>>
>> # to get the p-value
>> > summary(lm.D9)$coefficients["groupTrt","Pr(>|t|)"]
>> [1] 0.2490232
>>
>> [End quote]
>>
>> However, this does not seem to work with mle2, and the methods you  
>> suggested this time don't allow me access to the "etc" (the  
>> standard error and its probability for example). Is there a way to  
>> do this similar to what you suggested for lm, where I can at  
>> anything reported by mle2?
>>
>> Tom
>>
>>
>> David Winsemius wrote:
>>> On Jan 31, 2009, at 9:13 PM, Tom La Bone wrote:
>>>>
>>>> The mle2 function (bbmle library) gives an example something like  
>>>> the
>>>> following in its help page. How do I access the coefficients,  
>>>> standard
>>>> errors, etc in the summary of "a"?
>>> ?coef
>>> ?vcov
>>> eeep. Further comment on "etc" not possible at this time. Mind  
>>> reading equipment malfunction.
>
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