[R] glm inside one self-defined function

[Bill.Venables at csiro.au]

Mike Wolfgang asks:

>
> From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Mike Wolfgang
> Sent: Wednesday, 23 August 2006 1:31 PM
> To: R-help list
> Subject: [R] glm inside one self-defined function
> 
> Hi list,
> 
> I've searched in R-help and found some related discussions but still
could
> not understand this type of error. My own function is pretty complex,
so I
> would not put it here, but the basic algorithm is like this:
> myfun<-function(k){
>   mydata<-...#by someway I create a data frame
>   mymodel<-glm(y~.,family=binomial(),data=mydata)
>   ...#some other stuff
> }

I think you are leaving out something.  Here is a test of what you
claim gives a problem (R 2.3.1, Windows):

    > myfun <- function(n) {
    +   z <- rnorm(n)
    +   mydata <- data.frame(x = z, 
    +     y = rbinom(n, size = 1, prob = exp(z)/(1+exp(z))))
    +   fm <- glm(y ~ x, binomial, mydata)
    +   fm
    + }
    > 
    > myfun(100)
    
    Call:  glm(formula = y ~ x, family = binomial, data = mydata) 
    
    Coefficients:
    (Intercept)            x  
    	 0.1587       1.0223  
    
    Degrees of Freedom: 99 Total (i.e. Null);  98 Residual
    Null Deviance:      137.6 
    Residual Deviance: 118.3        AIC: 122.3 

Not even a murmur of complaint.  (This also works in S-PLUS 7.0 but
earlier versions of S-PLUS gave a problem rather like the one you note,
curiously.)

Look again at your code and see if the abstract version you give
really matches what you did, may I suggest?

> 
> as I execute this function, it gives error like this
> Error in inherits(x, "data.frame") : object "mydata" not found
> 
> So I guess glm here tries to find "mydata" in the parent environment.
Why
> doesn't it take "mydata" inside the function? How to let glm correctly
> locate it? Is this (scope/environment) mentioned in R manual? Thanks,
> 
> Mike