On Fri, 27 Jun 2008, Dan Bolser wrote:
Please consider the following PCA example;
my.df <-
data.frame(A=(x <- rnorm(100,mean=100, sd=10)),
B=(y <- x + rnorm(100,mean=10, sd=10)))
plot(my.df)
my.pc <-
prcomp(my.df, center=TRUE, scale=TRUE)
biplot(my.pc)
my.x <- (my.pc$x)[,1]
my.y <- (my.pc$x)[,2]
plot(my.x, my.y, type="n")
text(my.x, my.y, labels=1:100)
Clearly the plots have the same relative values, but I can't work out how
the second plot is relative to the first. I have been reading the manual,
but I still can't work it out.
Can anyone show me the code to generate the data that I see plotted using
biplot? What am I missing?
Reading the references on ?biplot.prcomp, or a good book on the subject
(such as MASS or Gower & Hand).
A biplot is a specific type of plot and the help page does not spell out
the rather mathematical details (and there are several variants).
Dan.
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Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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