Hi Baptisti,
Sorry for the late reply. I wanted to thank you for putting me on the
right track. I finally got something to work not really by extracting
the legend from a xyplot call, but by building my own legend grid.frame
and passing it to my low-level function. Understanding Grobs and
grid.pack took me some time, but now, it is working like a charm.
Thank again to you (and to Paul Murrell for the grid package!)
Sebastien
baptiste auguie wrote:
Hi,
I don't know if it helps, but looking at the output of xyplot you can
extract the legend (a grid.frame) as follows,
library(grid)
library(lattice)
p = xyplot(x~y, group=x,data=data.frame(x=1:10,y=1:10),
auto.key=list(space="right"))
legend = with(p$legend$right, do.call(lattice:::drawSimpleKey, args))
grid.draw(legend)
and lattice::draw.key might also help if you need to customize the legend.
HTH,
baptiste
2009/10/22 Sebastien Bihorel <sebastien.biho...@cognigencorp.com>:
Dear R-Users,
I would like to have the opinion of the list on the following matter. I have
this generic function that creates multiple lattice scatterplots per page
based upon different subsets of the same dataset. The use of different
line/point colors/symbols in each plot is based upon a 'group' variable',
which is the same for all plots. My goal is to create a main legend per
page:
1- because the 'group' variable' is the same for all plots, one legend per
page is sufficient;
2- because the subset of data used for a particular scatterplot does not
have to contain all unique elements of the group variable in the whole
dataset, the graphical settings need to be adjusted for each plot based upon
a general list of settings created from the whole dataset prior to the
creation of the plots;
3- for the same reason, I cannot use the key argument of xyplot to create a
legend from the first scatterplot.
Another piece of info is that this generic function could be used to create
very different categories of graphs, which each require a different legend
design.
At the moment, I am creating the legend based upon the general graph
settings and the category of plot. Prior to the creation of the graphs, I
store grid objects (text, point, line, or rectangle) into a list, with also
some information about the number of lines that the legend will use, and the
category of the plot. After the plots are printed to the device, I open a
viewport at the bottom of my page and split it according to the type of the
graph and the number of lines it needs. Finally, I just loop through the
content of the list and draw the grid objects.
Overall, this is all fine but a bit 'brute force'. Also the final
'open-a-viewport-and-draw-inside' step is a big messy code within a generic
graph function, because one specific piece of code is needed per category of
plot, and because of additional subtleties (conditional argument, etc... )
Based upon the behavior of the xyplot function, I understand that it would
be possible to store the fully formatted legend directly at its creation and
then just 'print' the stored object within my legend viewport. Could anybody
advise me on the process to follow to accomplish that or maybe a few
functions to look at?
As always, any help would be greatly appreciated.
Sebastien
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