R help - Oct 2007 - ggplot2 geom_hline error

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


-- 
================================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

On 10/14/07, Jim Nikelski <jnikelski at gmail.com>
wrote:
> 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"
Can you try the following?

plt + geom_hline(aes(group=1), intercept = 0)

If that works, I'll fix it in the development version.
>   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.
The axis label is a property of the scale, so you set it by overriding
the default scale:

plot + scale_y_continuous("New y axis label")

Hadley

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