R help - Feb 2008 - Optional data argument for a function

Dear All,

I am working on a function that has an optional data argument, just like lm().
If the user sets the data argument equal to some dataframe, then the function
should look inside the dataframe for the variables given to other arguments,
otherwise the variables should be accessible from what I believe is called the
parent frame from which the function was called. I looked at the source code for
lm() (and similar functions) and the documentation of ?eval, but I just
can't quite figure out how to make this work.

So, for a simple example, suppose I want to do this with the following function:

dosomething <- function(x, data) {
	temp <- x^2 + 5
	return(temp)
}

How does the function need to be changed, so that dosomething(somevariable,
data=somedataframe) will find somevariable within the dataframe somedataframe
and if dosomething(somevariable) is called, the function should find
somevariable in the parent frame (or anywhere else in the search path)?

Thanks for any help!

-- 
Wolfgang Viechtbauer 
?Department of Methodology and Statistics 
?University of Maastricht, The Netherlands 
?http://www.wvbauer.com/

One option is:

dosomething <- function(x, data, env=parent.frame()) {
       if(!missing(data)) x <- data[,deparse(substitute(x))]
       temp <- x^2 + 5
       return(temp)
}

On 29/02/2008, Viechtbauer Wolfgang (STAT)
<Wolfgang.Viechtbauer at stat.unimaas.nl> wrote:
> Dear All,
>
>  I am working on a function that has an optional data argument, just like
lm(). If the user sets the data argument equal to some dataframe, then the
function should look inside the dataframe for the variables given to other
arguments, otherwise the variables should be accessible from what I believe is
called the parent frame from which the function was called. I looked at the
source code for lm() (and similar functions) and the documentation of ?eval, but
I just can't quite figure out how to make this work.
>
>  So, for a simple example, suppose I want to do this with the following
function:
>
>  dosomething <- function(x, data) {
>         temp <- x^2 + 5
>         return(temp)
>  }
>
>  How does the function need to be changed, so that
dosomething(somevariable, data=somedataframe) will find somevariable within the
dataframe somedataframe and if dosomething(somevariable) is called, the function
should find somevariable in the parent frame (or anywhere else in the search
path)?
>
>  Thanks for any help!
>
>  --
>  Wolfgang Viechtbauer
>   Department of Methodology and Statistics
>   University of Maastricht, The Netherlands
>   http://www.wvbauer.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.
>

-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O