R help - Dec 2003 - : global and local variables

Hi all

   I have a problem pertaining to local and global variables.

   Say I have a function defined as follows:

   a<-function(x)
   {y<x^2}

   i.e
   a(2)
   [1] 4

   function b is now defined to take the value of y and do some
   manipulation with it. As it stands I dont know how to store the
   variable y such that other functions are able to reference its value.

   I know that I can simply put the operations found in b simply into a
   but this is not what I want.

   I would like to have stand alone functions say

   a, b and c which could be run independently as well as have a function
   called say

   control that can run a, b and c.

   i.e.

   control<- function( x)
   {
   a(x)
   b(x)
   c(x)
   }

   I hope that you guys understand what I'm trying to do.

   Cheers
   Allan

allan clark wrote:
>    Hi all
> 
>    I have a problem pertaining to local and global variables.
> 
>    Say I have a function defined as follows:
> 
>    a<-function(x)
>    {y<x^2}
> 
>    i.e
>    a(2)
>    [1] 4
The function a specified above won't return 4!


>    function b is now defined to take the value of y and do some
>    manipulation with it. As it stands I dont know how to store the
>    variable y such that other functions are able to reference its value.
> 
>    I know that I can simply put the operations found in b simply into a
>    but this is not what I want.
> 
>    I would like to have stand alone functions say
> 
>    a, b and c which could be run independently as well as have a function
>    called say
> 
>    control that can run a, b and c.
> 
>    i.e.
> 
>    control<- function( x)
>    {
>    a(x)
>    b(x)
>    c(x)
>    }
> 
>    I hope that you guys understand what I'm trying to do.
You are trying to read "An Introduction to R"???
If not, please try!

What you are really going to do: using assigments and return() 
statements as in:

a <- function(x) return(x^2)

foo <- function(x) {
   y <- a(x)
   z <- b(x)
   return(list(y=y, z=z))
}

foo(.....)

Uwe Ligges

>    Cheers
>    Allan
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help

Hi!

I'm no guru in R. But I can think of 2 ways (have to
be tried):

1) As Uwe Ligges said: just save return the stored
variable a<-preprocess(xdata) and return it (if you
want to return more than 1 item use list) and give
this variable to the next function. Example:

func1<-function(x) 
{
y<-x^2
# for testing:
print(paste("func1", x, y))
return(y) 
}

func2<-function(x, valuefunc1=NA)
{
if (is.na(valuefunc1)) valuefunc1<-func1(x)
# calculate things with valuefunc1
print(paste("func2", x, valuefunc1))
return(list(valuefunc1=valuefunc1))
}

func3<-function(x, valuefunc1=NA)
{
if (is.na(valuefunc1)) valuefunc1<-func1(x)
# calculate things with valuefunc1
print(paste("func3", x, valuefunc1))
return(list(valuefunc1=valuefunc1))
}

# use this
a<-list(NA)
names(a)<-c("valuefunc1")

a<-func2(x=3, valuefunc1=a$valuefunc1)
a<-func3(x=3, valuefunc1=a$valuefunc1) # be careful,
makes only sense if the x is equal to former fuction
call...
a<-func3(x=999, valuefunc1=a$valuefunc1) # will be the
same
a<-func3(x=999) # will be different 


2) use global variables like
assign("stored.value", x, envir=.GlobalEnv)
example see reply of my posting:
RE: [R] LOCF - Last Observation Carried Forward Simon
Fear (Sat 15 Nov 2003 - 03:28:03 EST) 

HTH,
Karl