Question

I think I’m getting a scoping error when using transformBy(), part of the doBy package for R. Here is a simple example of the problem:

> library(doBy)
>
> test.data = data.frame(
+  herp = c(1,2,3,4,5),
+  derp = c(2,3,1,3,5)
+ )
>
> transformData = function(data){
+ 
+  five = 5
+ 
+  transformBy(
+   ~ herp,
+   data=data,
+   sum=herp + derp + five
+  )
+ }
>
> transformData(test.data)
Error in eval(expr, envir, enclos) : object 'five' not found

When I run transformBy() within a sub-scope (non-global scope) no local variables or functions seem to be available for use in transformBy. If, on the other hand, I define those variables or functions globally, they become available. Here is a slightly modified example that works:

> library(doBy)
>
> test.data = data.frame(
+  herp = c(1,2,3,4,5),
+  derp = c(2,3,1,3,5)
+ )
>
> five = 5
>
> transformData = function(data){
+  transformBy(
+   ~ herp,
+   data=data,
+   sum=herp + derp + five
+  )
+ }
>
> transformData(test.data)
  herp derp sum
1    1    2   8
2    2    3  10
3    3    1   9
4    4    3  12
5    5    5  15

Am I misunderstanding something about how transformBy is supposed to work or is something broken?

Versions:

• ubuntu: 8.04 (x64)
• R: 2.10.1
• doBy: 4.0.5

Answer 1

This is clearly documented in the ?transformBy help page, and therefore
not a bug.

Details:

 The ... arguments are tagged vector expressions, which are
 evaluated in the data frame data. The tags are matched against
 names(data), and for those that match, the value replace the
 corresponding variable in data, and the others are appended to
 data.

Simply make the object “five” a part of the data.frame “data”, and
it will work as you expect. Currently the function is trying to
evaluate “five” in the “data” data.frame, which fails of course.