R help - May 2003 - again troubles with lattice

Dear r-help community,

  Thank you for your previous answers!
  
  Now I have strange behaviour of the lattice library funcitons.
  They do not draw graphics in the file when called from the script.
  I created the script file, called, for example, "a.R", containing
  the following
  
library(lattice);
trellis.device(device="png",
               filename="a.png",
               color = FALSE,
               bg = "white",
               width=600,
               height=800
              );

xyplot(ac15$value~ac15$year|factor(lon),data=ac15,
       type="o",
       layout=c(1,18),
       xlab="year",
       );
dev.off();


The structure of ac15 data frame is like following
year    value    lon
1979  93.428747  0
1979  87.298608  20
1979  78.506340  40
...
1979  45.567890  340
1980  60.815289  0
1980  49.630904  20
1980  24.981362  40
...

I execute command source("a.R") it works and after its running
I've
got file a.png in the working directory. But it contains only white
background field and no graphs.

If I try copy commands of the script in clipboard and paste them to
the R console the graphs appear in the file.

-- 
Best regards
Wladimir Eremeev                                     mailto:wl at eimb.ru

On Thu, 8 May 2003, Wladimir Eremeev wrote:
> Dear r-help community,
> 
>   Thank you for your previous answers!
>   
>   Now I have strange behaviour of the lattice library funcitons.
>   They do not draw graphics in the file when called from the script.
>   I created the script file, called, for example, "a.R",
containing
>   the following
They do when called from a script running directly.  It's calling the 
script file from source() that gives the problem.

You haven't actually asked for anything to be plotted!  xyplot returns a
plottable object, which when *printed* is plotted.  Auto-printing works at
the top level in R, but not inside source.  You need to wrap your lattice
calls in print().

[...]
> I execute command source("a.R") it works and after its running
I've
> got file a.png in the working directory. But it contains only white
> background field and no graphs.
> 
> If I try copy commands of the script in clipboard and paste them to
> the R console the graphs appear in the file.
And that is `running the script'.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

On Thursday 08 May 2003 03:54 am, Wladimir Eremeev
wrote:
> Dear r-help community,
>
>   Thank you for your previous answers!
>
>   Now I have strange behaviour of the lattice library funcitons.
>   They do not draw graphics in the file when called from the script.
>   I created the script file, called, for example, "a.R",
containing
>   the following
>
> library(lattice);
> trellis.device(device="png",
>                filename="a.png",
>                color = FALSE,
>                bg = "white",
>                width=600,
>                height=800
>               );
>
> xyplot(ac15$value~ac15$year|factor(lon),data=ac15,
>        type="o",
>        layout=c(1,18),
>        xlab="year",
>        );
> dev.off();
You have to print the result of xyplot, which does not happen inside another 
function unless you explicitly call print().

This is obviously somewhat confusing because base R graphics does not behave 
this way, and has led to many similar questions on this list. help(xyplot) 
has:

Value:

     An object of class ``trellis''. The `update' method can be used
to
     update components of the object and the `print' method (usually
     called by default) will plot it on an appropriate plotting device.


and help(Lattice) has:


Note:

     High level Lattice functions (like `xyplot') are different from
     conventional S graphics functions because they don't actually draw
     anything. Instead, they return an object of class ``trellis''
     which has to be then `print'ed. This often causes confusion when
     the high level functions are called inside another function (most
     often `source') and hence don't produce any output.


Can you suggest any other place in the documentation where explaining this 
would have helped you find it ?

Deepayan

It might be helpful to include a brief comment on the need for
an implicit or explicit call to print() in the information that 
is displayed by typing help(package=lattice)
It might be an extra sentence under Description:
> Date: Thu, 8 May 2003 10:05:40 -0500
> From: Deepayan Sarkar <deepayan at stat.wisc.edu>
> Subject: Re: [R] again troubles with lattice
> To: Wladimir Eremeev <wl at eimb.ru>, r-help at stat.math.ethz.ch
> 
>.....
> 
> Can you suggest any other place in the documentation where explaining this 
> would have helped you find it ?
> 
> Deepayan
John Maindonald                     email : john.maindonald at anu.edu.au
Centre for Bioinformation Science,  phone : (6125)3473        
c/o MSI,                            fax   : (6125)5549 
John Dedman Mathematical Sciences Building (Building 27)
Australian National University
Canberra ACT 0200
Australia