% File src/library/datasets/man/trees.Rd
% Part of the R package, http://www.R-project.org
% Copyright 1995-2007 R Core Team
% Distributed under GPL 2 or later

\name{trees}
\docType{data}
\alias{trees}
\title{Girth, Height and Volume for Black Cherry Trees}
\description{
  This data set provides measurements of the girth, height and volume
  of timber in 31 felled black cherry trees.  Note that girth is the
  diameter of the tree (in inches) measured at 4 ft 6 in above the
  ground.
}
\usage{trees}
\format{
  A data frame with 31 observations on 3 variables.
  \tabular{rlll}{
    \code{[,1]} \tab \code{Girth} \tab numeric
    \tab Tree diameter in inches\cr
    \code{[,2]} \tab \code{Height}\tab numeric
    \tab Height in ft\cr
    \code{[,3]} \tab \code{Volume}\tab numeric
    \tab Volume of timber in cubic ft\cr}
}
\source{
  Ryan, T. A., Joiner, B. L. and Ryan, B. F. (1976)
  \emph{The Minitab Student Handbook}.
  Duxbury Press.
}
\references{
  Atkinson, A. C. (1985)
  \emph{Plots, Transformations and Regression}.
  Oxford University Press.
}
\examples{
require(stats); require(graphics)
pairs(trees, panel = panel.smooth, main = "trees data")
plot(Volume ~ Girth, data = trees, log = "xy")
coplot(log(Volume) ~ log(Girth) | Height, data = trees,
       panel = panel.smooth)
summary(fm1 <- lm(log(Volume) ~ log(Girth), data = trees))
summary(fm2 <- update(fm1, ~ . + log(Height), data = trees))
step(fm2)
## i.e., Volume ~= c * Height * Girth^2  seems reasonable
}
\keyword{datasets}