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
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