# R help for question 9 in Topic 8

# first we read in the dataset iris.txt
# variables are Species, SpecCode, SepLen, SepWd, PetLen, PetWd, LD

data=read.table("http://bayes.bgsu.edu/m400/data/iris1.txt",
  header=T,sep="\t")

# here's a plot of sepal length against width for two species of iris

attach(data)
plot(SepWd[Species=="Setosa"],SepLen[Species=="Setosa"],
  xlim=c(1.8,4.2),ylim=c(4,7.2),xlab="SepWd",ylab="SepLen")
points(SepWd[Species=="Versicolor"],SepLen[Species=="Versicolor"],pch=19)
legend("topright",legend=c("Setosa","Versicolor"),pch=c(1,19))

# I'm adding a line with interecept .877 and slope 1.477 to the 
# current graph -- this corresponds to the linear discrimintor.

abline(a=.877,b=1.477)

# Maybe a more direct way to see the separation is to compute
# values of LD and construct a dotplot of LD against species.

LD= 0.877 - SepLen + 1.477 * SepWd
stripchart(LD ~ Species,pch=19,method="stack")