R help - Dec 2008 - Non-interactive passing of quoted variables (ggplot, plyr, subset, transform, etc)

Hello Everyone,
May be a silly question.

How to pass programmatically variables which are not known in advance and  
are quoted? Variables are quoted implicitly in  functions like
"subset"
and "transform" and explicitly in ggplot and plyr.

For instance I would like to have something like this:

myfunc<-functon(mydata,X) subset(mydata,X>4)
myfunc<-function(mydata,X,Y) {ggplot(mydata,aes(x=X,y=Y))+geom_points()}

this does not work since X and Y are not in mydata.

Many, many thanks,
Vitalie.

On Mon, Dec 1, 2008 at 11:06 AM, Vitalie Spinu <vitosmail at rambler.ru>
wrote:
> Hello Everyone,
> May be a silly question.
>
> How to pass programmatically variables which are not known in advance and
> are quoted? Variables are quoted implicitly in  functions like
"subset" and
> "transform" and explicitly in ggplot and plyr.
>
> For instance I would like to have something like this:
>
> myfunc<-functon(mydata,X) subset(mydata,X>4)
> myfunc<-function(mydata,X,Y) {ggplot(mydata,aes(x=X,y=Y))+geom_points()}
For subset, just do it by hand:

mydata[mydata[[X]] > 4, ]

For ggplot, see aes_string:

aes_string(x = X, y = Y)
which will do what you want

For plyr, you can use a character vector:

ddply(mtcars, c("cyl"), colwise(mean))
ddply(mtcars, c("cyl ^ 2", "vs - am"), colwise(mean))

In general you need to use substitute or bquote.

Hadley

-- 
http://had.co.nz/