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Jon Zadra

2010-Oct-13 18:19 UTC

[R] Change global env variables from within a function

Hi,

I've looked all over for a solution to this, but haven't had much look 
in specifying what I want to do with appropriate search terms.  Thus I'm 
turning to R-help.

In the process of trying to write a simple function to rename individual 
column names in a data frame, I ran into the following problem: When I 
rename the columns within my function, I can't seem to get it to apply 
to the data frame in the global environment in a simple manner.

Given:

tempdf <- data.frame("a" = 1:6, "b" = 7:12)

#I can rename a to g this way:
names(tempdf)[names(tempdf)=="a"] <- "g"

#Wanting to simplify this for the future, I have the function:
colrename <- function(dframe, oldname, newname) {
     names(dframe)[names(dframe)==oldname] <- newname
     }

colrename(tempdf, "a", "g")

#However of course the change to tempdf stays within colrename().  I 
could add "return(names(dframe))" to the function and then call the 
function like:
#names(tempdf) <- colrename(tempdf, "a", "g")
#but at that point its not much simpler than the original:
#names(tempdf)[names(tempdf)=="a"] <- "g"

So, i'm wondering, is there a way to write code within that function so 
that the tempdf in the global environment gets changed?
I thought of doing "names(dframe)[names(dframe)==oldname] <<-
newname"
but then of course it doesn't replace "dframe" with
"tempdf" in the
evaluation, so it seems to be a problem of looking at some variables 
within the function environment but others in the parent environment.

Any help is greatly appreciated.

Thanks,

Jon
-- 
Jon Zadra
Department of Psychology
University of Virginia
P.O. Box 400400
Charlottesville VA 22904
(434) 982-4744
email: zadra at virginia.edu
<http://www.google.com/calendar/embed?src=jzadra%40gmail.com>

Duncan Murdoch

2010-Oct-13 18:28 UTC

head link

[R] Change global env variables from within a function

On 13/10/2010 2:19 PM, Jon Zadra wrote:>    Hi,
>
> I've looked all over for a solution to this, but haven't had much
look
> in specifying what I want to do with appropriate search terms.  Thus
I'm
> turning to R-help.
>
> In the process of trying to write a simple function to rename individual
> column names in a data frame, I ran into the following problem: When I
> rename the columns within my function, I can't seem to get it to apply
> to the data frame in the global environment in a simple manner.
>
> Given:
>
> tempdf<- data.frame("a" = 1:6, "b" = 7:12)
>
> #I can rename a to g this way:
> names(tempdf)[names(tempdf)=="a"]<- "g"
>
> #Wanting to simplify this for the future, I have the function:
> colrename<- function(dframe, oldname, newname) {
>       names(dframe)[names(dframe)==oldname]<- newname
>       }
>
> colrename(tempdf, "a", "g")
>
> #However of course the change to tempdf stays within colrename().  I
> could add "return(names(dframe))" to the function and then call
the
> function like:
> #names(tempdf)<- colrename(tempdf, "a", "g")
> #but at that point its not much simpler than the original:
> #names(tempdf)[names(tempdf)=="a"]<- "g"
>
> So, i'm wondering, is there a way to write code within that function so
> that the tempdf in the global environment gets changed?
> I thought of doing "names(dframe)[names(dframe)==oldname]<<-
newname"
> but then of course it doesn't replace "dframe" with
"tempdf" in the
> evaluation, so it seems to be a problem of looking at some variables
> within the function environment but others in the parent environment.
>
> Any help is greatly appreciated.

Make the changes to a local copy, then save it to the global (or just 
return the local copy as the value of the global).  For example,

colrename<- function(dframe, oldname, newname) {
      names(dframe)[names(dframe)==oldname]<- newname
      dframe
      }

called as

tempdf<- colrename(tempdf, "a", "g")

or if you really want to mess with things that don't belong to your
function,



colrename<- function(dframe, oldname, newname) {
      name<- deparse(substitute(dframe))
      names(dframe)[names(dframe)==oldname]<- newname
      assign(name, dframe, env=globalenv())
      }



(but watch out if you call this with something other than a simple 
variable name as the first argument).

Duncan Murdoch

Erik Iverson

2010-Oct-13 18:49 UTC

head link

[R] Change global env variables from within a function

Hello,

Jon Zadra wrote:>  Hi,
> 
> I've looked all over for a solution to this, but haven't had much
look
> in specifying what I want to do with appropriate search terms.  Thus
I'm
> turning to R-help.
> 
> In the process of trying to write a simple function to rename individual 
> column names in a data frame, I ran into the following problem: When I 
> rename the columns within my function, I can't seem to get it to apply 
> to the data frame in the global environment in a simple manner.
Not a direct answer to your question, but
does the ?rename function in the reshape package do what you want?

In general, the paradigm that I think R tries to promote is to
call functions that *return values* that you can assign to object
names, so calling "colrename" below to change an object in the
global environment is warned against for its side effects.

You could have the function return the modified data.frame, but
of course that's what the "rename" function I mention above does
already.

You might also see ?transform.
> 
> Given:
> 
> tempdf <- data.frame("a" = 1:6, "b" = 7:12)
> 
> #I can rename a to g this way:
> names(tempdf)[names(tempdf)=="a"] <- "g"
> 
> #Wanting to simplify this for the future, I have the function:
> colrename <- function(dframe, oldname, newname) {
>     names(dframe)[names(dframe)==oldname] <- newname
>     }
> 
> colrename(tempdf, "a", "g")
> 
> #However of course the change to tempdf stays within colrename().  I 
> could add "return(names(dframe))" to the function and then call
the
> function like:
> #names(tempdf) <- colrename(tempdf, "a", "g")
> #but at that point its not much simpler than the original:
> #names(tempdf)[names(tempdf)=="a"] <- "g"
> 
> So, i'm wondering, is there a way to write code within that function so
> that the tempdf in the global environment gets changed?
> I thought of doing "names(dframe)[names(dframe)==oldname] <<-
newname"
> but then of course it doesn't replace "dframe" with
"tempdf" in the
> evaluation, so it seems to be a problem of looking at some variables 
> within the function environment but others in the parent environment.
> 
> Any help is greatly appreciated.
> 
> Thanks,
> 
> Jon

Greg Snow

2010-Oct-13 19:36 UTC

head link

[R] Change global env variables from within a function

R is primarily a function language not a macro language and what you are trying
to do matches more with macro programming.

The best approach is to think functionally and learn the more Rish ways of doing
things (have the function return the changed data and the caller does the
replacement, like has been shown in other responses).

If you really want the macro behavior (and are willing to live with the
consequences (don't complain that you were not warned)), then look at the
defmacro function in the gtools package and the article in the reference section
on its help page.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Jon Zadra
> Sent: Wednesday, October 13, 2010 12:20 PM
> To: r-help at r-project.org
> Subject: [R] Change global env variables from within a function
> 
>   Hi,
> 
> I've looked all over for a solution to this, but haven't had much
look
> in specifying what I want to do with appropriate search terms.  Thus
> I'm
> turning to R-help.
> 
> In the process of trying to write a simple function to rename
> individual
> column names in a data frame, I ran into the following problem: When I
> rename the columns within my function, I can't seem to get it to apply
> to the data frame in the global environment in a simple manner.
> 
> Given:
> 
> tempdf <- data.frame("a" = 1:6, "b" = 7:12)
> 
> #I can rename a to g this way:
> names(tempdf)[names(tempdf)=="a"] <- "g"
> 
> #Wanting to simplify this for the future, I have the function:
> colrename <- function(dframe, oldname, newname) {
>      names(dframe)[names(dframe)==oldname] <- newname
>      }
> 
> colrename(tempdf, "a", "g")
> 
> #However of course the change to tempdf stays within colrename().  I
> could add "return(names(dframe))" to the function and then call
the
> function like:
> #names(tempdf) <- colrename(tempdf, "a", "g")
> #but at that point its not much simpler than the original:
> #names(tempdf)[names(tempdf)=="a"] <- "g"
> 
> So, i'm wondering, is there a way to write code within that function so
> that the tempdf in the global environment gets changed?
> I thought of doing "names(dframe)[names(dframe)==oldname] <<-
newname"
> but then of course it doesn't replace "dframe" with
"tempdf" in the
> evaluation, so it seems to be a problem of looking at some variables
> within the function environment but others in the parent environment.
> 
> Any help is greatly appreciated.
> 
> Thanks,
> 
> Jon
> --
> Jon Zadra
> Department of Psychology
> University of Virginia
> P.O. Box 400400
> Charlottesville VA 22904
> (434) 982-4744
> email: zadra at virginia.edu
> <http://www.google.com/calendar/embed?src=jzadra%40gmail.com>
> 
> ______________________________________________
> 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.

David Winsemius

2010-Oct-13 20:01 UTC

head link

[R] Change global env variables from within a function

On Oct 13, 2010, at 2:19 PM, Jon Zadra wrote:
> Hi,
>
> I've looked all over for a solution to this, but haven't had much  
> look in specifying what I want to do with appropriate search terms.   
> Thus I'm turning to R-help.
>
> In the process of trying to write a simple function to rename  
> individual column names in a data frame, I ran into the following  
> problem: When I rename the columns within my function, I can't seem  
> to get it to apply to the data frame in the global environment in a  
> simple manner.
There already is a function (or perhaps a composition of two  
functions) that does what you ask. It's the '<-' method for
names()
usually invoked in its dyadic form:

names(object) <- character_vector

 > df <- data.frame(one=rnorm(10), two=rnorm(10))
 > names(df) <- c("three", "four")
 > names(df)
[1] "three" "four"

In your case it would work like this:

 > names(tempdf)[ which(names(tempdf)=="a") ] <- "g"
 > names(tempdf)
[1] "g" "b"

-- 
David.
>
> Given:
>
> tempdf <- data.frame("a" = 1:6, "b" = 7:12)
>
> #I can rename a to g this way:
> names(tempdf)[names(tempdf)=="a"] <- "g"
>
> #Wanting to simplify this for the future, I have the function:
> colrename <- function(dframe, oldname, newname) {
>    names(dframe)[names(dframe)==oldname] <- newname
>    }
>
> colrename(tempdf, "a", "g")
>
> #However of course the change to tempdf stays within colrename().  I  
> could add "return(names(dframe))" to the function and then call
the
> function like:
> #names(tempdf) <- colrename(tempdf, "a", "g")
> #but at that point its not much simpler than the original:
> #names(tempdf)[names(tempdf)=="a"] <- "g"
>
> So, i'm wondering, is there a way to write code within that function  
> so that the tempdf in the global environment gets changed?
> I thought of doing "names(dframe)[names(dframe)==oldname] <<-  
> newname" but then of course it doesn't replace "dframe"
with
> "tempdf" in the evaluation, so it seems to be a problem of
looking
> at some variables within the function environment but others in the  
> parent environment.
>
> Any help is greatly appreciated.
>
> Thanks,
>
> Jon
> -- 
> Jon Zadra
> Department of Psychology
> University of Virginia
> P.O. Box 400400
> Charlottesville VA 22904
> (434) 982-4744
> email: zadra at virginia.edu
> <http://www.google.com/calendar/embed?src=jzadra%40gmail.com>
>
> ______________________________________________
> 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.
David Winsemius, MD
West Hartford, CT

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