On 11-04-09 7:02 PM, Spencer Graves wrote:
On 4/9/2011 2:31 PM, Hadley Wickham wrote:
On Sat, Apr 9, 2011 at 2:51 PM, Paul Johnson<pauljoh...@gmail.com> wrote:
Years ago, I did lots of Perl programming. Perl will let you be lazy
and write functions that refer to undefined variables (like R does),
but there is also a strict mode so the interpreter will block anything
when a variable is mentioned that has not been defined. I wish there
were a strict mode for checking R functions.
Here's why. We have a lot of students writing R functions around here
and they run into trouble because they use the same name for things
inside and outside of functions. When they call functions that have
mistaken or undefined references to names that they use elsewhere,
then variables that are in the environment are accidentally used. Know
what I mean?
dat<- whatever
someNewFunction<- function(z, w){
#do something with z and w and create a new "dat"
# but forget to name it "dat"
lm (y, x, data=dat)
# lm just used wrong data
}
I wish R had a strict mode to return an error in that case. Users
don't realize they are getting nonsense because R finds things to fill
in for their mistakes.
Is this possible? Does anybody agree it would be good?
library(codetools)
checkUsage(someNewFunction)
<anonymous>: no visible binding for global variable ‘y’
<anonymous>: no visible binding for global variable ‘x’
<anonymous>: no visible binding for global variable ‘dat’
Which also picks up another bug in your function ;)
Is this run by "R CMD check"? I've seen this message.
"R CMD check" will give this message sometimes when I don't feel
it's appropriate. For example, I define a data object ETB in a package,
then give that as the default in a function call like
f(data.=ETB){if(missing(data.))data(ETB); data.}. When I run "R CMD
check", I get "no visible binding for global variable 'ETB'", even
though the function is tested and works during R CMD check.
What is ETB? Your code is looking for a global variable by that name,
and that's what codetools is telling you.
Duncan Murdoch
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