biplot.princomp
Produces a biplot (in the strict sense) from the output of
princomp
or prcomp
 Keywords
 multivariate, hplot
Usage
# S3 method for prcomp
biplot(x, choices = 1:2, scale = 1, pc.biplot = FALSE, …)# S3 method for princomp
biplot(x, choices = 1:2, scale = 1, pc.biplot = FALSE, …)
Arguments
 x
 an object of class
"princomp"
.  choices
 length 2 vector specifying the components to plot. Only the default is a biplot in the strict sense.
 scale

The variables are scaled by
lambda ^ scale
and the observations are scaled bylambda ^ (1scale)
wherelambda
are the singular values as computed byprincomp
. Normally0 <= scale <= 1
, and a warning will be issued if the specifiedscale
is outside this range.  pc.biplot

If true, use what Gabriel (1971) refers to as a "principal component
biplot", with
lambda = 1
and observations scaled up by sqrt(n) and variables scaled down by sqrt(n). Then inner products between variables approximate covariances and distances between observations approximate Mahalanobis distance.  …
 optional arguments to be passed to
biplot.default
.
Details
This is a method for the generic function biplot
. There is
considerable confusion over the precise definitions: those of the
original paper, Gabriel (1971), are followed here. Gabriel and
Odoroff (1990) use the same definitions, but their plots actually
correspond to pc.biplot = TRUE
.
Side Effects
a plot is produced on the current graphics device.
References
Gabriel, K. R. (1971). The biplot graphical display of matrices with applications to principal component analysis. Biometrika, 58, 453467. Gabriel, K. R. and Odoroff, C. L. (1990). Biplots in biomedical research. Statistics in Medicine, 9, 469485.
See Also
Examples
library(stats)
require(graphics)
biplot(princomp(USArrests))