R help - Mar 2012 - Ggplot barchart drops factor levels: how to show them with zero counts?

Hello,

When plotting a barchart with ggplot it drops the levels of the factor for
which no counts are available.

For example:

library(ggplot)
mtcars$cyl<-factor(mtcars$cyl)
ggplot(mtcars[!mtcars$cyl==4,], aes(cyl))+geom_bar()
levels(mtcars[!mtcars$cyl==4,])

This shows my problem. Because no counts are available for factorlevel
'4',
the label 4 dissapears from the plot. However, I would still like it to show
up, but without a bar (zero observations).

I would like to use this for the presentation of data with a Likert-like
scale.

Thanks in advance!
Bart

--
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Sent from the R help mailing list archive at Nabble.com.

One possibility: update to ggplot2. The original ggplot isn't even on
CRAN any longer.

When I tried your example with ggplot2, the empty bar for 4 was
plotted as you'd expect.

Thanks for the small reproducible example.

Sarah

On Thu, Mar 15, 2012 at 11:47 AM, Bart6114 <bartsmeets86 at gmail.com>
wrote:
> Hello,
>
> When plotting a barchart with ggplot it drops the levels of the factor for
> which no counts are available.
>
> For example:
>
> library(ggplot)
> mtcars$cyl<-factor(mtcars$cyl)
> ggplot(mtcars[!mtcars$cyl==4,], aes(cyl))+geom_bar()
> levels(mtcars[!mtcars$cyl==4,])
>
> This shows my problem. Because no counts are available for factorlevel
'4',
> the label 4 dissapears from the plot. However, I would still like it to
show
> up, but without a bar (zero observations).
>
> I would like to use this for the presentation of data with a Likert-like
> scale.
>
> Thanks in advance!
> Bart
>
-- 
Sarah Goslee
http://www.functionaldiversity.org

You can tell that levels must not be dropped with scale_x_discrete():

library(ggplot2)
mtcars$cyl<-factor(mtcars$cyl)
plot1 <- ggplot(mtcars[!mtcars$cyl==4,], aes(cyl))+geom_bar()
plot1 + scale_x_discrete(drop=FALSE)

Or explicitly set the values you want in the x axis with the argument
"limits":

plot1 + scale_x_discrete(limits=levels(mtcars$cyl))


Regards,
Helios

>>> El d?a 15/03/2012 a las 16:47, Bart6114 <bartsmeets86 at
gmail.com>
escribi?:
> Hello,
> 
> When plotting a barchart with ggplot it drops the levels of the
factor for
> which no counts are available.
> 
> For example:
> 
> library(ggplot)
> mtcars$cyl<-factor(mtcars$cyl)
> ggplot(mtcars[!mtcars$cyl==4,], aes(cyl))+geom_bar()
> levels(mtcars[!mtcars$cyl==4,])
> 
> This shows my problem. Because no counts are available for
factorlevel '4',
> the label 4 dissapears from the plot. However, I would still like it
to show
> up, but without a bar (zero observations).
> 
> I would like to use this for the presentation of data with a
Likert-like
> scale.
> 
> Thanks in advance!
> Bart
> 
> --
> View this message in context: 
>
http://r.789695.n4.nabble.com/Ggplot-barchart-drops-factor-levels-how-to-show-the
> m-with-zero-counts-tp4475417p4475417.html
> Sent from the R help mailing list archive at Nabble.com.
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