R help - Nov 2010 - ggplot2: facet_grid with different vertical lines on each facet

Hello,

I am plotting many histograms together using facet_grid in ggplot2. However,
I want to then add a vertical line to each histogram, or facet, each of
which vertical lines are at different x-values.

The following example adds all vertical lines to each facet:
ggplot(data,aes(values)) + geom_histogram() + facet_grid(.~variable) +
geom_vline(xintercept=c(5,10,15))

How can I add a vertical line at different x positions on each facet?

Thanks very much,
Scott Chamberlain

	[[alternative HTML version deleted]]

Hi Scott,
You can put the vline data in a separate data.frame:

dat <- data.frame(x=rnorm(20), y=rnorm(20), z=rep(c("a",
"b"), each=10))

vline.dat <- data.frame(z=levels(dat$z), vl=c(0,1))

library(ggplot2)

ggplot(dat, aes(x=x, y=y)) +
 geom_point() +
 geom_vline(aes(xintercept=vl), data=vline.dat) +
 facet_grid(.~z)

Best,
Ista

On Tue, Nov 9, 2010 at 4:41 PM, Scott Chamberlain <schamber at rice.edu>
wrote:
> Hello,
>
> I am plotting many histograms together using facet_grid in ggplot2.
However,
> I want to then add a vertical line to each histogram, or facet, each of
> which vertical lines are at different x-values.
>
> The following example adds all vertical lines to each facet:
> ggplot(data,aes(values)) + geom_histogram() + facet_grid(.~variable) +
> geom_vline(xintercept=c(5,10,15))
>
> How can I add a vertical line at different x positions on each facet?
>
> Thanks very much,
> Scott Chamberlain
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org