[R] passing function parameters into a 'with' statement to dynamically pick out columns

[peter dalgaard]

On Jun 20, 2012, at 16:45 , David Marx wrote:

> Hi,
> 
> I've built a function to generate plots and would like to be able pass in column names as a parameter. Here's a boiled down version of what I have right now:
> 
> pmts <- data.frame(date=c(1,2,3), all=c(5,6,7),maj=c(4,5,6),ind=c(3,4,5))
> perc.mktshare <- function(df){  
>  range1 <- floor(min(with(df, 100*ind/all)))
>  range2 <- ceiling(max(with(df, 100*ind/all)))  
>  with(df,plot(date,100*ind/all,ylim=c(range1,range2),ylab="% Marketshare"))
> }
> perc.mktshare(pmts)
> 
> What I'd like to do is something like this:
> 
> perc.mktshare <- function(df, scaling.column){  
>  range1 <- floor(min(with(df, 100*scaling.column/all)))
>  range2 <- ceiling(max(with(df, 100*scaling.column/all)))  
>  with(df,plot(date,100*"scaling.column"/all,ylim=c(range1,range2),ylab="% Marketshare"))
> }
> perc.mktshare(pmts,"ind")
> perc.mktshare(pmts,"maj")
> 
> I've tried going about this a couple of different ways but I can't make it work. My suspicion is that there's probably no way to do this using the 'with' statement and I'll have to trim the input dataframe to the pertinent columns first using subset or something.
> 

Something with eval(bquote(.....)) should do it, e.g.

foo <- function(col) eval(bquote(with(airquality, plot(.(col), Ozone))))
foo(quote(Wind))
foo(quote(Solar.R))

Or, use .(as.name(col)) inside bquote, and foo("Wind") in the call.

Possibly, substitute() can be used as well, but it might get tricky.



> Thanks for your help!
> 
> David
> 
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-- 
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com