[R] ggplot2 geom_hline error

[Jim Nikelski]

Hello R-List

    I've run  into a minor problem with ggplot2. In particular, I get
an error message when trying to plot a horizonal line through zero.
Here is what I do:

plt.df <- subset(xfm.df, select=c(stage, subj, tX))
plt <- ggplot(pp.df, aes(x=stage, y=tX, group=subj)) + geom_line()
plt
plt <- plt + geom_hline(intercept=0)
plt

  The first plot yields a most lovely graph. Addition of the
geom_hline yields ...

"Error in eval(expr, envir, enclos) : object "subj" not found"

The data.frame that I'm plotting looks like this ...

> str(plt.df)
'data.frame':	468 obs. of  3 variables:
 $ stage: Factor w/ 12 levels "f1","f2","f3",..: 1 1 1 1 1 1 1 1 1 1 ...
 $ subj : Factor w/ 39 levels "1","2","3","4",..: 1 2 3 4 5 6 7 8 9 10 ...
 $ tX   : num  -0.00011 -0.44548 -0.39649 -0.19610 -0.46434 ...


   I suspect that I'm likely doing something obviously wrong, but I
can't figure out what it might be.  Any suggestions?


  On an unrelated note, does anyone know how I might change the
default axis names in ggplot? I suspect it's aes-related, but not
quite sure.

Thanks,


-Jim


-- 
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Jim Nikelski, Ph.D.
Postdoctoral Research Fellow
Bloomfield Centre for Research in Aging
Lady Davis Institute for Medical Research
Sir Mortimer B. Davis - Jewish General Hospital
McGill University