Hello listservers.

I have a question.  Is there a way to use different symbols for data  
points of different categories (i.e. to represent a 3rd variable,  
which is a factor) when using trellis graphics?  I am plotting a  
continuous variable v. a factor using the stripplot function (lattice  
package), because I want each data point represented on the plot.  but  
i would like to represent a third, factor variable by making those  
data points in different symbols according to this variable.  any  
guidance on how to do this would be much appreciated.  the reason i am  
using trellis graphics is that i want the individual points to be  
plotted by treatment, rather than having a boxplot, as the base  
graphics package would plot with a continuous variable ~ a factor  
variable.

an example of my data and the command i am using follows.

dataset is called data
response variable (y-axis) is FishLength, a continuous variable
predictor variable (x-axis)  is Treatment, a factor
third variable, which i would like to be represented via the shape of  
the data point, is Stream, a factor

so far I can only plot the data points against the treatment.

  stripplot(FishLength ~ Treatment, ylab="", xlab="", jitter=TRUE,  
data=data, col="black")

how can i now represent Stream with different shaped data points?

thank you,
bessie

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bessie Green Markley
M.S. Candidate, Dept. of Biology and Wildlife
Alaska Cooperative Fish and Wildlife Research Unit
Institute of Arctic Biology
Sheenjek trailer, N. Koyukuk Drive
University of Alaska Fairbanks 99775
907-474-1949




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