On 11/10/2009 11:14 AM, Stefan Zeugner wrote:
Hello,
After hours of googling I could not resolve the following (although it
seems simple):
I would like to put subfunctions in a separate .R file that is then
called with source() from inside several "main" functions. A crude
example would be as follows:
**** file subtest.R **********
subtest <- function() {
foo <<- foo+1
}
******************************
*** main function ************
test<-function(foo) {
source("test.R",local=TRUE)
subtest()
return(foo)
}
******************************
Then executing the code
> test(1)
works as prescribed.
But of course, each function call to test() 'sources' (i.e. parse() and
eval()) the file subtest.R again and again. (try e.g. changing line 2 in
subtest.R to 'foo<<- foo +2' and run 'test(1)' )
How can I 'attach' the function subtest inside the main function, such
that it is not evaluated again at each function call?
Just declaring it there is the only reasonable way, i.e.
test<-function(foo) {
subtest <- function() {
foo <<- foo+1
}
subtest()
return(foo)
}
The reason you can't somehow assign it within an existing test is that
subtest is a different closure every time. Its environment will be the
local frame of the call to test, so the "foo" on the right hand side of
the assignment will be the value that was passed to test.
An unreasonable way to get what you want is to mess with the
environment, e.g.
subtest <- function() {
foo <<- foo+1
}
test <- function(foo) {
mysubtest <- subtest # make a local copy
environment(mysubtest) <- environment() # attach the local frame
mysubtest()
return(foo)
}
This is ugly programming, likely to bite you at some future date.
Duncan Murdoch
And this while maintaining the above 'subfunction' functionality (i.e.
attaching the subfunction under the right environment)?
I was not able to resolve that - thanks in advance for any help!
all the best
Stefan
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and provide commented, minimal, self-contained, reproducible code.
