[R] biplot.princomp with loadings only

[Jari Oksanen]

On Thu, 2004-09-30 at 10:33, Christoph Lehmann wrote:
> Hi
> 
> is there a way to plot only the loadings in a biplot (with the nice 
> arrows), and to skip the scores?
> 
Christoph,

I may have overlooked some email messages, but it seems to me that you
haven't yet got an answer to your practical question. From the practical
point of view, we may skip the point that you rather ask for a
"monoplot" than "biplot" if you have only one set of points. Further, I
may forget my surprise when I see that somebody really thinks that these
arrows are "nice". OK, they may be nice if you have only a couple of
them, but anybody plotting 30 or more arrows normally asks how to get
rid off this mess. 

Of course you can plot arrows in your "monoplot", since you have got
access to everything in R and you can do anything with R (but coffee
comes somewhat bland, so I recommend something else for the task cooking
coffee). Here is an example:

# Run PCA
data(USArrests)
sol <- princomp(USArrests, cor=T)
# Extract loadings
X <- sol$loadings
# Plot the frame
plot(X, asp=1, type="n")
abline(v=0, lty=3)
abline(h=0, lty=3)
# Plot arrows: see ?arrows for the syntax
arrows(0, 0, X[,1], X[,2], len=0.1, col="red")
# Label the arrows
text(1.1*X, rownames(X), col="red", xpd=T)

Cheers, jari okanen
-- 
Jari Oksanen <jarioksa at sun3.oulu.fi>