[R] Problem with facet_grid in ggplot2

[Brian Diggs]

On 4/11/2011 9:33 AM, Simon Hayward wrote:
> Hi all,
>
> I am practising a bit with ggplot2 but I have a problem when I try to
> use facet_grid.
>
> The following code:-
>
> p<- ggplot(diamonds, aes(carat, ..density..)) +
> + geom_histogram(binwidth = 1)
>
> p + facet_grid(cut ~ clarity, margins=TRUE)
>
> produce the following error:-
>
> Error in class(output[[var]])<- class(value) :
>    cannot set class to "array" unless the dimension attribute has length
>> 0
>
> I have lifted this code directly from the ggplot2 documentation!
>
> By a process of elimination it seems that the problem arises from the
> use of margins.
>
> I do not know why the dimension attribute is conflicting with margins
> unless it is something to do with the properties of the data frame.
>
> I am running R 2.12.1
>
> Has the source code changed?
>
> Very grateful for any help
>
> Simon Hayward

Simon,

You have correctly figured out the problem; the margins argument does 
not work in facet_grid.  It is a known bug.  See, for example,

http://groups.google.com/group/ggplot2/browse_thread/thread/8a49a200ac3172a7
http://groups.google.com/group/ggplot2/browse_thread/thread/97ba6e2f469792cc

It is still there in ggplot2 0.8.9 (the latest release).

-- 
Brian S. Diggs, PhD
Senior Research Associate, Department of Surgery
Oregon Health & Science University