R help - Jun 2013 - Functions within functions - environments

Dear list,


I have a problem with nested functions and I don't manage to get it
solved. I know I should be looking in environments, and I have tried a
lot, but it keeps on erroring. 
An easy version of the problem is as follows:



innerfunction<-function()
{
    print(paste(a, " from inner function"))
    print(paste(b, " from inner function"))
    setwd(wd)
}


middlefunction<-function()
{
    b="b"
    print(paste(b, " from middle function"))
    innerfunction()
}


outerfunction<-function()
{
    a="a"
    print(paste(a," from outer function"))
    middlefunction()
}

outerfunction()



Here, R will tell me that the inner function has no clue what a or b is.
So what I want, is the inner function to recognize a and b.
Any suggestions?

Many thanks!
Rik




-- 
________________________________________________

Rik Verdonck



Research group of Molecular Developmental Physiology and Signal
Transduction
KULeuven, Faculty of Science
Naamsestraat 59,  Bus 02465
B-3000 Leuven,Belgium
Tel. +32 16 32 39 65
Fax +32 16 32 39 02

http://bio.kuleuven.be/df/JV/index2.htm
rik.verdonck@bio.kuleuven.be





      Please consider the environment before printing this e-mail

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Hello,

See the help page for parent.frame, and use its argument to go back to 
the frames of variables 'a' and 'b':


innerfunction<-function()
{
     env1 <- parent.frame(1)  # for 'b'
     env2 <- parent.frame(2)  # for 'a'
     print(paste(env2$a, " from inner function"))
     print(paste(env1$b, " from inner function"))
     setwd(wd)
}


Now it complains about 'wd'.
(Are you sure you want to hard code the number of frames to go back to? 
It seems better to write "normal" functions, i.e., functions with 
arguments. innerfunction would have 2 args and middlefunction just one, 
'a'.)

Hope this helps,

Rui Barradas

Em 12-06-2013 18:42, Rik Verdonck escreveu:
> Dear list,
>
>
> I have a problem with nested functions and I don't manage to get it
> solved. I know I should be looking in environments, and I have tried a
> lot, but it keeps on erroring.
> An easy version of the problem is as follows:
>
>
>
> innerfunction<-function()
> {
>      print(paste(a, " from inner function"))
>      print(paste(b, " from inner function"))
>      setwd(wd)
> }
>
>
> middlefunction<-function()
> {
>      b="b"
>      print(paste(b, " from middle function"))
>      innerfunction()
> }
>
>
> outerfunction<-function()
> {
>      a="a"
>      print(paste(a," from outer function"))
>      middlefunction()
> }
>
> outerfunction()
>
>
>
> Here, R will tell me that the inner function has no clue what a or b is.
> So what I want, is the inner function to recognize a and b.
> Any suggestions?
>
> Many thanks!
> Rik
>
>
>
>

A function looks up free variables in the environment in which the function
was defined, not in the environment in which the function was called.  The
latter is called something like 'dynamic scoping' and usually leads to
trouble,
the former is 'lexical scoping' and leads to predictable results.  You
can do
dynamic scoping in R (using get(), assign(), and parent.frame()), but it
leads to code that only works correctly in favorable circumstances.  You should
pass
data from the caller to the callee via the argument list, not via free
variables.

To use lexical scoping define your functions as:

outerfunction<-function()
{
     middlefunction<-function()
     {
          innerfunction<-function()
          {
              print(paste(a, " from inner function"))
              print(paste(b, " from inner function"))
              # setwd(wd) # wd was not defined in your mail
        }
        b="b"
        print(paste(b, " from middle function"))
        innerfunction()
     }
     a="a"
     print(paste(a," from outer function"))
     middlefunction()
}
> outerfunction()
[1] "a  from outer function"
[1] "b  from middle function"
[1] "a  from inner function"
[1] "b  from inner function"

(One can change the environment of a function after it is defined, but
there is not often a need to do that.)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org] On Behalf
> Of Rik Verdonck
> Sent: Wednesday, June 12, 2013 10:42 AM
> To: r-help at r-project.org
> Subject: [R] Functions within functions - environments
> 
> Dear list,
> 
> 
> I have a problem with nested functions and I don't manage to get it
> solved. I know I should be looking in environments, and I have tried a
> lot, but it keeps on erroring.
> An easy version of the problem is as follows:
> 
> 
> 
> innerfunction<-function()
> {
>     print(paste(a, " from inner function"))
>     print(paste(b, " from inner function"))
>     setwd(wd)
> }
> 
> 
> middlefunction<-function()
> {
>     b="b"
>     print(paste(b, " from middle function"))
>     innerfunction()
> }
> 
> 
> outerfunction<-function()
> {
>     a="a"
>     print(paste(a," from outer function"))
>     middlefunction()
> }
> 
> outerfunction()
> 
> 
> 
> Here, R will tell me that the inner function has no clue what a or b is.
> So what I want, is the inner function to recognize a and b.
> Any suggestions?
> 
> Many thanks!
> Rik
> 
> 
> 
> 
> --
> ________________________________________________
> 
> Rik Verdonck
> 
> 
> 
> Research group of Molecular Developmental Physiology and Signal
> Transduction
> KULeuven, Faculty of Science
> Naamsestraat 59,  Bus 02465
> B-3000 Leuven,Belgium
> Tel. +32 16 32 39 65
> Fax +32 16 32 39 02
> 
> http://bio.kuleuven.be/df/JV/index2.htm
> rik.verdonck at bio.kuleuven.be
> 
> 
> 
> 
> 
>       Please consider the environment before printing this e-mail
> 
> 	[[alternative HTML version deleted]]
> 
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