> On Feb 12, 2016, at 10:33 AM, Jacob Wegelin <jacobwege...@fastmail.fm> wrote:
>
> To check that a regression object comes from logistic regression, I employ
> the following two lines:
>
> stopifnot(glmObject$family$family=="binomial")
>
> stopifnot(glmObject$family$link=="logit")
>
> For instance:
>
> toyfunction<-function(glmObject) {
> stopifnot(inherits(glmObject, "glm"))
> stopifnot(glmObject$family$family=="binomial")
> stopifnot(glmObject$family$link=="logit")
> cat("okay, I guess\n")
> glmObject
> }
>
> mydata <- read.csv("http://www.ats.ucla.edu/stat/data/binary.csv";)
>
> someobject<- glm(admit~gre+gpa, data=mydata)
>
> toyfunction(someobject)
>
> someobject<- glm(admit~gre+gpa, data=mydata, family="binomial")
>
> toyfunction(someobject)
>
> But Doug Bates once stated that it's preferable to use extractor functions
> (and perhaps other ready-made functions?) rather than "deconstructing" an
> object (his term), as I do here.
>
> Accordingly, is there a smarter way to perform the check that I perform
> inside toyfunction?
>
> Thanks for any insight
>
> Jacob A. Wegelin
Hi Jacob,
The rationale behind Doug's comment is that if there is a pre-existing
extractor function, you are at less risk due to future possible changes in the
underlying object structure, than if you try to access an object element
directly.
If the underlying object structure should change in the future, you never know
what result you might get by accessing the element directly, if you get one at
all.
If you use the extractor function, that would be (or should be) modified to
reflect the change in the underlying object.
For your examples above, ?family should work, but returns more than just the
'family' and 'link' components, which print.family() displays:
someobject<- glm(admit~gre+gpa, data=mydata)
> family(someobject)
Family: gaussian
Link function: identity
someobject<- glm(admit~gre+gpa, data=mydata, family="binomial")
> family(someobject)
Family: binomial
Link function: logit
So, you could feasibly use:
family(someobject)$family
family(someobject)$link
and so forth, to perform your checks. If you look at the output of
str(family(someobject)), you will see the other elements contained.
Regards,
Marc Schwartz
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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.
