R help - Aug 2010 - ggplot2 barplot: extra markers in graph

Dear List,

(self-contained example + version info at the bottom)

I'm having trouble producing a barplot using the functions in ggplot2. When
I use the position="dodge" option, the bars are plotted  but also a
number of spurious markers. More specifically, a number of black dots are
plotted in the graph that should not be there. This behaviour is not seen when
calling the same functions without the position="dodge".

Can someone shed some light on this? How can I avoid this?

#self-contained example:
library(ggplot2)
D<-runif(30)
N<-rep(c(1:10),3)
C<-rep(c(1:3),10)
DT<-data.frame(D=D,N=N,C=C)
#works ok
qplot(DT$N,DT$D,fill=factor(DT$C))+  geom_bar(stat = "identity")
#in the resulting plot, a number of black markers are added that should not be
there
qplot(DT$N,DT$D,fill=factor(DT$C))+  geom_bar(stat = "identity",
position="dodge")
#end of example

version info:
Windows xp 64
R version 2.11.1 (64 bit)
ggplot2 version 0.8.8

On Aug 4, 2010, at 7:52 AM, Dieter Vanderelst wrote:
> Dear List,
>
> (self-contained example + version info at the bottom)
>
> I'm having trouble producing a barplot using the functions in  
> ggplot2. When I use the position="dodge" option, the bars are  
> plotted  but also a number of spurious markers. More specifically, a  
> number of black dots are plotted in the graph that should not be  
> there. This behaviour is not seen when calling the same functions  
> without the position="dodge".
>
> Can someone shed some light on this? How can I avoid this?
>
> #self-contained example:
> library(ggplot2)
> D<-runif(30)
> N<-rep(c(1:10),3)
> C<-rep(c(1:3),10)
> DT<-data.frame(D=D,N=N,C=C)
> #works ok
> qplot(DT$N,DT$D,fill=factor(DT$C))+  geom_bar(stat = "identity")
> #in the resulting plot, a number of black markers are added that  
> should not be there
> qplot(DT$N,DT$D,fill=factor(DT$C))+  geom_bar(stat = "identity",
> position="dodge")
> #end of example
>
Happens on a Mac, too (OSX 10.5.8, R 2.11.1, ggplot2 0.8.8 )

If you just want to make the dots go away, you can use:

qplot(DT$N,DT$D,fill=DT$C, geom = "bar",  
stat="identity",position="dodge")

But you should probably also report it to Hadley.

> version info:
> Windows xp 64
> R version 2.11.1 (64 bit)
> ggplot2 version 0.8.8

-- 
David Winsemius, MD
West Hartford, CT

The reason you see the exra markers is that the first part of the command
"qplot(DT$N,DT$D,fill=factor(DT$C))" already plots the individual
points.
You didn't see it with "geom_bar(stat = "identity")"
simply because the
stacked bars made the previous layer invisible. To see this you can use the
ggplot function to reproduce your graph (with the points):

p<-ggplot(data=DT,aes(x=N,y=D))+geom_point()+geom_bar(stat="identity",aes(fill=factor(C)),position="dodge")

print(p)

It then becomes obvious that once you omit the geom_point(), the points are
gone. 

This is IMO a feature of the ggplot2 system, not necessarily a bug.


-- 
View this message in context:
http://r.789695.n4.nabble.com/ggplot2-barplot-extra-markers-in-graph-tp2313337p2313426.html
Sent from the R help mailing list archive at Nabble.com.