Alan,
Doesn't Peter Dalgaard's response get you what you originally asked for? You
said you wanted something like:
> if (1) { c <- 1; foo <- function () print(c); }
>c <- 2
>foo()
Based on Peter's email you could do
> c <- 1
> foo <- local({x <- c; function() print(x) })
> foo()
[1] 1
> c <- 2
> foo()
[1] 1
Hope this is helpful,
Dan
Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
> Behalf Of William Dunlap
> Sent: Thursday, July 02, 2009 2:44 PM
> To: Allan Engelhardt
> Cc: r-help@r-project.org
> Subject: Re: [R] How to use current value of variable in function definition?
>
>
>
>
> ________________________________
>
> From: Allan Engelhardt [mailto:all...@cybaea.com]
> Sent: Thursday, July 02, 2009 11:12 AM
> To: William Dunlap
> Cc: r-help@r-project.org
> Subject: Re: [R] How to use current value of variable in
> function definition?
>
>
> Thanks for the pointer to substitute(), William. This seems to
> work and is a little shorter than yours:
>
> a <- 1; foo <- eval(substitute(function () print(a),
> env=list(a=a)))
> a <- 2; foo()
> # [1] 1
>
> Not the clearest code I have ever seen, especially as 'foo'
> still shows 'a':
>
> print(foo)
> # function () a
>
> Allan
>
> The need for eval and the misleading printout is why I sent the
> longer version.
> functionBody(foo) does show the right thing. One might consider
> this a bug
> in substitute(): it does not clear out the source information
> when it works on
> a call to function. You can add
> attr(foo,"source")<-NULL
> to fix up the printing.
>
> substitute() doesn't seem to go into the default values of the
> arguments,
> which is where one might prefer to put variables like this.
>
> The eval() around substitute() is needed because function(z)z+1
> is a call to
> a function called function, it is not a function until that call
> gets evaluated
> and substitute does not evaluate its first argument).
>
> Using local() avoids these problems.
> Bill Dunlap
> TIBCO Software Inc - Spotfire Division
> wdunlap tibco.com
>
>
>
> On 02/07/09 18:28, William Dunlap wrote:
>
> From: r-help-boun...@r-project.org
> [mailto:r-help-boun...@r-project.org] On Behalf
> Of Allan Engelhardt
> Sent: Thursday, July 02, 2009 9:47 AM
> To: r-help@r-project.org
> Subject: [R] How to use current value of
> variable in function
> definition?
>
> Must be the heat or something but I can't get my
> brain into gear and
> figure out how to get something like
>
> if (1) { c <- 1; foo <- function () print(c); }
> c <- 2
> foo()
>
> to print 1, not 2. (The real life example is a
> little more
> complex, but
> you get the idea. I don't want the variable c
> in the function
> definition, I want its value at that time.)
>
> The only thing I have been able to come up with
> is something like
>
> if (1) foo <- (function () { c <- 1;
> return(function () print(c)) })()
> c <- 2
> foo()
> # [1] 1
>
>
> You might try local(), as in
> > c<-1 ; foo.local<-local({orig.c <- c ;
> function()orig.c})
> > foo.local()
> [1] 1
> > c<-3
> > foo.local()
> [1] 1
> It is possible for someone to alter the orig.c after you
> create
> foo.local, as in
> > assign("orig.c", 17, env=environment(foo.local))
> > foo.local()
> [1] 17
> Looking at the function's code will not make it clear
> where
> orig.c is coming from. The clue is that its environment
> is not
> one of the standard named ones, but it given by a hex
> number.
> > foo.local
> function()orig.c
> <environment: 0x02108c54>
>
> You could also use substitute() to change the code in
> the function.
> It can be messy to do but the resulting code may be
> clearer (although
> it won't give a hint as to where that constant came
> from). E.g.,
> > foo.substitute<-function()orig.c
> > c<-1 ;
> functionBody(foo.substitute)<-do.call(substitute,
> list(functionBody(foo.substitute), list(orig.c=c)))
> > foo.substitute()
> [1] 1
> > foo.substitute
> function ()
> 1
>
> Bill Dunlap
> TIBCO Software Inc - Spotfire Division
> wdunlap tibco.com
>
>
>
> but that just hurts. Please make the pain go
> away.
>
> Can someone wake up my brain?
>
> Allan.
>
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained,
> reproducible code.
>
>
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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