[R] scoping problem?

[Jonathan Qiang Li]

Hi, 

I wrote a dummy function that passes a dataset to tree() as the
following:

test.func <- function(training.data){
	tr <- tree(type~., data = training.data)
	tr
}

Then I run the function under R

> test.func(MyData)

Error in model.frame.default(formula = type ~ ., data = training.data) : 
	Object "training.data" not found

MyData resides in the working environment, while training.data does not.
R manual
claims that scoping of free variables are "lexical" (Introduction to R,
chapter 10.7).
 I take that it means that in evaluating the expression 
tree(type~., data=training.data) ,
R will look in the scope of the function test.func, therefore
discovering "training.data" 
as a "formal parameter". But it seemed that I misunderstood something
here. 

I also made a global variable 

> training.data <- MyData

and run 

> test.func(MyData) 

The function works fine without complaints.

Can someone please help with this matter?

Jonathan
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