[R] biplot

[Peter Lauren]

I have started using biplot() (with R1.3.0 on Windows) and have become very
frustrated.  As far as I can see, I follow the directions but either it
doesn't do what I want it to do, it gives fairly arcane error messages or
both.  All I want to do is plot two separate data sets to see how different
they are from each other with respect to two metrics that are represented by
the two axes. 

My first problem is that biplot forms two axes: the bottom and left axes for
the former data set and the top and right axes for the latter set. 
Invariably, these axes are scaled differently so it look like the data sets
are easy to distinguish until I realise that they are plotted on different
axes.  I try to make all the axes the same by doing

>  biplot(former_set, latter_set,xlim <- 0:3,ylim <- 0:3)

This sets the left and bottom axes to the required range but not the top or
right axis.

I also do not want the arrow heads, so I enter

>   biplot(former_set, latter_set,arrow.len=0)

I do not get the arrows but I do get the following error message.
Error in arrows(x0, y0, x1, y1, length = length, angle = angle, code = code,
: 
        invalid head length

This depite the fact that the help for biplot says " The arrow head can be
suppressed by `arrow.len = 0'.".  

The program also does not appear to like it when I enter 

>    biplot(former_set, latter_set,var.axis=FALSE,colour)

I get 11 warnings, all saying 'parameter "var.axis" couldn't be set in
high-level plot() function' but the graph does not look any different.

Also, colour does not appear to work.  I fill a vector, colour, with
different numbers and check them with 

> colour

to get

> [1] 3 2

but the colours are always black and red regardless of which numbers I
enter.

I would be most grateful if someone could enlighten me on how to fix these
problems.

Thanks,
Peter.





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