[R] Dynamic regex/sub changes to function

[Daniel Fuka]

Thanks everyone for the help. I need to step back and refresh my
memory on expressions as I am still unclear as to why I can not
directly edit:
body(nsong)[[2]]
# Which can be located from a grep:
body(nsong)[[grep("fuka",body(nsong))]]
# though I believe
class(body(nsong)[[2]])
[1] "="
# is trying to give me a pretty blatant hint... {: -)

On Mon, Sep 22, 2014 at 1:24 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 22/09/2014 11:34 AM, Daniel Fuka wrote:
>>
>> Howdy Duncan,
>>
>> Thanks for the quick reply!  I must be missing something
>> simple/obvious. I need to have the "sub()" not return quoted and
>> escaped characters to "just edit the language expression". In my
>> problem, there is a function that is supported from a different
>> package. So I always want to use the supported function as my base...
>> but a url in the supported function needs to be changed dynamically
>> for my application, which is easiest using "sub()".
>>
>> I am trying to do what you correctly indicate I would need to do:
>> "just edit the language expression that body(fsong) gives you, and
>> assign it back"
>> BUT, using sub, I get back a quoted string in my example if I just use
>> sed:
>>
>> > fsong
>> function(x){
>>   song=paste("my name is fuka,",x)
>>   return(song)
>> }
>> # Using "sub()" becomes:
>> > nsong
>> function (x)
>> {
>>      "song = paste(\"my name is muka,\", x)"
>>      return(song)
>> }
>
>
> You didn't do it right :-).   With fsong as above, the string to edit is
> body(fsong)[[c(2,3,2)]].  (Why c(2,3,2)?  Because that's where the string is
> in the parse tree.  Try looking at variations on body(fsong)[[c(2,3,2)]] to
> figure it out, e.g.
> body(fsong)[[c(2,3)]], or body(fsong)[[c(2,3,3)]], etc.)
>
> So this code would work:
>
> orig <- body(fsong)[[c(2,3,2)]]
> new <- sub("fuka", "muka", orig)
>
> # Now put it back in nsong:
> nsong <- fsong
> body(nsong)[[c(2,3,2)]] <- new
>
> But as Bill said, this is a really bad idea.  If you just *think* about
> changing that fsong function, it will break.
>
> Duncan Murdoch
>
>>
>> Thanks again for the quick reply and help you are giving me!
>> dan
>>
>> On Mon, Sep 22, 2014 at 10:37 AM, Duncan Murdoch
>> <murdoch.duncan at gmail.com> wrote:
>> > On 22/09/2014 9:16 AM, Daniel Fuka wrote:
>> >>
>> >> Howdy,
>> >>
>> >> I have searched the lists and can not seem to find a solution to my
>> >> problem. I need to be able to dynamically modify a string inside a
>> >> function to build a new function. "sub" replaces with a quoted
>> >> string... and "parse" of "sub" returns expression... How can I get an
>> >> unquoted string from a regex to stick into a "body" of a function?
>> >
>> >
>> > It's possible to do what you want, though you don't want to be using
>> > parse(), you can just edit the language expression that body(fsong)
>> > gives
>> > you, and assign it back.  But that's a messy way to solve your problem.
>> >
>> > Why not create a new function containing the new string?  e.g.
>> >
>> > makefsong <- function(name = "fuka") {
>> >   line1 <- paste("my name is", name)
>> >   function(x) {
>> >     song <- paste(line1, x)
>> >     return(song)
>> >   }
>> > }
>> >
>> > f1 <- makefsong()
>> > f1("I live on the second floor")
>> > f2 <- makefsong("muka")
>> > f2("I live on the second floor")
>> >
>> > Duncan Murdoch
>> >
>> >>
>> >> Thanks for your help!
>> >> dan
>> >>
>> >> # Original Function
>> >> fsong=function(x){
>> >>   song=paste("my name is fuka,",x)
>> >>   return(song)
>> >> }
>> >> fsong("I live on the second floor")
>> >> #
>> >> # Copy and modify using "sub" returns quoted string with escaped quotes
>> >> #   internally... as expected.. which can not be evaluated.
>> >> nsong=fsong
>> >> body(nsong)[[grep("fuka",body(nsong))]]=
>> >>     sub("fuka","muka",list(body(fsong)[[grep("fuka",body(fsong))]]))
>> >>
>> >> nsong("I live on the second floor") # broken
>> >>
>> >> #
>> >> # Copy and modify with "parse" of  "sub",  returns expression.. but
>> >> without quotes,
>> >> # o getting closer.
>> >> #
>> >> nsong=fsong
>> >> body(nsong)[[grep("fuka",body(nsong))]]=
>> >>
>> >>
>> >> parse(text=sub("fuka","muka",list(body(fsong)[[grep("fuka",body(fsong))]])))
>> >>
>> >> ______________________________________________
>> >> R-help at r-project.org mailing list
>> >> https://stat.ethz.ch/mailman/listinfo/r-help
>> >> PLEASE do read the posting guide
>> >> http://www.R-project.org/posting-guide.html
>> >> and provide commented, minimal, self-contained, reproducible code.
>> >
>> >
>
>