[R] ggplot2 used in a function - variable scope/environment

[Martin Rittner]

Hi everybody!

I'm trying to use ggplot2 to return a plot from a function (so I can add 
something or alter it then). Unfortunately, if I add a mapping to a 
layer in the function, the variable *name* is stored in the layer, 
rather than the variable's *value* - so that after the function returns 
the ggplot2-object, it doesn't plot because the variable don't exist in 
the environment calling the function.. e.g:

my function does something like:

getPlot<-function(da=NULL,...){	
	#1st column holds x-values, others hold data series to plot...
	co<-as.character(names(da))
	co<-co[2:length(co)]

	pl<-ggplot(data=da)
	pl<-pl+scale_y_log10()+scale_x_continuous()
	for(c in co){
		pl<-pl+geom_line(x=da[[1]],y=da[[c]],mapping=aes(x=da[[1]],y=da[[c]]))
	}

	return(pl)
}

I need to add every layer separately, because I want to be able to 
explicitly define attributes for every data series (colour, size... e.g. 
highlight only two specific out of 10 series...).

Anyway, my problem is this:

d<-data.frame(x=seq(0.0,1.0,length=5),y1=rnorm(5),y2=rnorm(5))
p<-getPlot(da=d)
p

returns with

Error in data.frame(..., check.names = FALSE) :
   arguments imply differing number of rows: 0, 5

and the plot object contains:

Title:
Labels:  x=, y=
-----------------------------------
Data:    x, y1, y2 [5x3]
Mapping:
Scales:  y,x -> y,x
$margins
[1] FALSE

$facets
[1] ". ~ ."

-----------------------------------
geom_line: (colour=black, size=1, linetype=1, x=NA, y=NA) + (x=c(0, 
0.25, 0.5, 0.75, 1), y=c(0.180036717548597, -0.369556903134046, 
-0.924474152821948, -2.40773640658189, 0.801471591443009))
stat_sort: (...=) + (x=c(0, 0.25, 0.5, 0.75, 1), y=c(0.180036717548597, 
-0.369556903134046, -0.924474152821948, -2.40773640658189, 
0.801471591443009))
position_identity: ()
mapping: (x=da[[1]], y=da[[c]])

geom_line: (colour=black, size=1, linetype=1, x=NA, y=NA) + (x=c(0, 
0.25, 0.5, 0.75, 1), y=c(-1.59744511956184, -0.9333541477049, 
1.88697835844878, 0.921829569181679, -0.741077741846118))
stat_sort: (...=) + (x=c(0, 0.25, 0.5, 0.75, 1), y=c(-1.59744511956184, 
-0.9333541477049, 1.88697835844878, 0.921829569181679, -0.741077741846118))
position_identity: ()
mapping: (x=da[[1]], y=da[[c]])

Note the mappings, they refer to "da" and "c" (defined in the function) 
which are not available in the calling environment. Any Idea how I can 
avoid the problem/paste the actual values in, like it did for the 
geometry and the statistics?

Thanks, Martin