Function to create variables with prefix

Hi.  I'm a new R user and think what I'm trying to do is pretty basic, but
haven't been able to find the answer in the mailing list archives.  How do I
write a function that creates new variables in a given data.frame with a
prefix attached to the variable names?  I do a lot of repetitive logging and
scaling of variables, and would like a way to consistently generate and name
versions of the variables.

The function would take a data.frame, an array of variables, and a prefix
string.  It performs a transformation on the variables (e.g. logs and
scales), and creates new variables with the same names as the inputs, but
with the prefix_string prepended.

So, a sample call would look like:

myfunction(mydata, myvariables, "norm_")

And if myvariables contained variables named "var1", "var2", etc., the
function would generate:

mydata$norm_var1
mydata$norm_var2

Thanks,
Moira

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Thanks to everyone who replied.  I really appreciate your help, and have
been trying variations on the solutions you've offered.  Unfortunately, none
do quite what I'm hoping to do.  Uwe's suggestion seems to be the closest (I
think), but the new variables created within the function didn't exist
outside of the scope of the function.  (If there's something basic in R that
I'm just missing, please let me know!)

Here's a rephrasing of what I'm trying to do:

Let's say I have a data.frame called mywidgets.  It has these variables:

mywidgets$length
mywidgets$width
mywidgets$height
mywidgets$color
mywidgets$country

And I have some subsets of mywidgets, let's say:  bluefrenchwidgets  and
redcanadianwidgets.  And I'm planning to make lots more subsets in the
future.  So I want to create a function that performs some operation (such
as scaling) within a subset easily.

The function would be called sort of like this:

sizeattributes <- c("length", "width", "height")
myfunction(bluefrenchwidgets, sizeattributes, "norm_")
myfunction(redcanadianwidgets, sizeattributes, "norm_")

And then a bunch of scaled variables would be created within those subsets,
e.g.:

bluefrenchwidgets$norm_length
redcanadianwidgets$norm_width
etc.

Can someone suggest either a function that will do this, or another way to
approach the problem?

Thanks,
Moira


On Tue, Jul 15, 2008 at 3:06 AM, Uwe Ligges <ligges at statistik.tu-dortmund.de>
wrote:

Example:

myfunction <- function(mydata, myvariables, prefix="norm_"){
       newnames <- paste(prefix, myvariables, sep="")
       mydata[newnames] <- scale(mydata[myvariables])
       mydata
}

mydata <- data.frame(a=1:2, b=3:2)
myfunction(mydata, c("a", "b"))


Moira Burke wrote:

Hi.  I'm a new R user and think what I'm trying to do is pretty basic, but
haven't been able to find the answer in the mailing list archives.  How do
I
write a function that creates new variables in a given data.frame with a
prefix attached to the variable names?  I do a lot of repetitive logging
and
scaling of variables, and would like a way to consistently generate and
name
versions of the variables.

The function would take a data.frame, an array of variables, and a prefix
string.  It performs a transformation on the variables (e.g. logs and
scales), and creates new variables with the same names as the inputs, but
with the prefix_string prepended.

So, a sample call would look like:

myfunction(mydata, myvariables, "norm_")

And if myvariables contained variables named "var1", "var2", etc., the
function would generate:

mydata$norm_var1
mydata$norm_var2

Thanks,
Moira

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