#
# Epage 231
#
# Written by:
# -- 
# John L. Weatherwax                2009-04-21
# 
# email: wax@alum.mit.edu
# 
# Please send comments and especially bug reports to the
# above email address.
# 
#-----

# version$language == "R" for R version$language == NULL for SPlus

if(is.null(version$language) == FALSE){ 
  require(alr3)
}else{
  library(alr3)
}

data(galapagos)

# lets replace the small elevation islands with 200m:
#
inds <- galapagos$EM==0
galapagos$Elevation[inds] <- 200.0

attach(galapagos)

# do some data analysis on the scatter plots of this data:
# 
postscript("../../WriteUp/Graphics/Chapter10/prob_7_pairs.eps", onefile=FALSE, horizontal=FALSE)
pairs(ES/NS~Area+Anear+Dist+DistSC+Elevation)
dev.off()

# transform some of the variables: Area and Anear
postscript("../../WriteUp/Graphics/Chapter10/prob_7_pairs_transformed.eps", onefile=FALSE, horizontal=FALSE)
pairs(log(ES/NS)~log(Area)+log(Anear)+Dist+DistSC+log(Elevation))
dev.off()

a <- galapagos
a$logESONS <- log(a$ES/a$NS)
a$logArea <- log(Area)
a$logAnear <- log(Anear)
a$logElevation <- log(Elevation)

# the simplest and most complicated model:
# 
m0 <- lm( logESONS ~ +1, data=a )
m1 <- lm( logESONS ~ +1+logArea+logAnear+Dist+DistSC+logElevation, data=a )

if(is.null(version$language) == FALSE) {require (xtable); xtable(m1)} else m1

# Lets start with forward selection for this problem:
#
ansf1 <- step(m0,scope=list(lower=~+1, upper=~+1+logArea+logAnear+Dist+DistSC+logElevation),
                direction="forward", data=a)

ansf2 <- step(m1,scope=list(lower=~+1, upper=~+1+logArea+logAnear+Dist+DistSC+logElevation),
                direction="backward", data=a)