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% File src/library/stats/man/screeplot.Rd
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% Part of the R package, http://www.R-project.org
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% Copyright 1995-2007 R Core Team
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% Distributed under GPL 2 or later
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\name{screeplot}
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\alias{screeplot}
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\alias{screeplot.default}
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\title{Screeplots}
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\usage{
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\method{screeplot}{default}(x, npcs = min(10, length(x$sdev)),
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          type = c("barplot", "lines"),
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          main = deparse(substitute(x)), \dots)
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}
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\arguments{
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  \item{x}{an object containing a \code{sdev} component, such as that
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    returned by \code{\link{princomp}()} and \code{\link{prcomp}()}.}
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  \item{npcs}{the number of components to be plotted.}
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  \item{type}{the type of plot.}
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  \item{main, \dots}{graphics parameters.}
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}
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\description{
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  \code{screeplot.default} plots the variances against the number of the
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  principal component. This is also the \code{plot} method for classes
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  \code{"princomp"} and \code{"prcomp"}.
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}
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\references{
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  Mardia, K. V., J. T. Kent and J. M. Bibby (1979).
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  \emph{Multivariate Analysis}, London: Academic Press.
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  Venables, W. N. and B. D. Ripley (2002).
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  \emph{Modern Applied Statistics with S}, Springer-Verlag.
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}
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\seealso{
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  \code{\link{princomp}} and \code{\link{prcomp}}.
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}
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\examples{
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require(graphics)
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## The variances of the variables in the
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## USArrests data vary by orders of magnitude, so scaling is appropriate
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(pc.cr <- princomp(USArrests, cor = TRUE))  # inappropriate
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screeplot(pc.cr)
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fit <- princomp(covmat = Harman74.cor)
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screeplot(fit)
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screeplot(fit, npcs = 24, type = "lines")
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}
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\keyword{multivariate}