[R] plotting prcomp

From: Dan Bolser <dan.bolser.r_at_googlemail.com>
Date: Fri, 27 Jun 2008 17:35:36 +0200


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?

Dan.

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