Cathedrals <- read.table('http://math.uttyler.edu/nathan/classes/statistics/data/cathedrals.data',header=TRUE)

Cathedrals[1:10,]
attach(Cathedrals)
plot(x,y,type='n',main='Cathedrals',xlab='height',ylab='length')
points(x[style=='r'],y[style=='r'],pch='r')
points(x[style=='g'],y[style=='g'],pch='g')
abline(lm(y~x),col='yellow')

abline(lm(y[style=='r']~x[style=='r']),col='pink',lty=2)
abline(lm(y[style=='g']~x[style=='g']),col='pink',lty=2)

goth = ifelse(style=='g',1,0)
m1 <- lm(y~x+goth+x*goth)
summary(m1)
# slopes same

m2 <- lm(y ~ x +goth)
summary(m2)

hot.dogs <- read.table('http://math.uttyler.edu/nathan/classes/statistics/data/hotdogs.data',header=TRUE)

hot.dogs