# R-program for Supplementary Exercises 2.12, 2.27, 2.28 and 2.60 of IPS7e

car <- read.csv("r:/Chapter 2/ex02_012.csv")
# scatterplot with fitted line
plot(car$speed, car$fuel)
abline( lsfit(car$speed, car$fuel))

# correlation
cor(car)
cor.test(~ speed+fuel, data=car)

# new variables
car$speed_mph <- car$speed/1.609
car$fuel_gpm <- car$fuel*(1.609/3.785)
car$milespergallon <- 1/car$fuel_gpm
cor(car)
plot(car$speed, car$milespergallon)
abline( lsfit(car$speed, car$milespergallon))

# 2.60: regression model
car.reg <- lm(fuel ~ speed, data=car)
summary(car.reg)
anova(car.reg)
car$resid <- residuals(car.reg)
sum(car$resid)
plot(car$speed, car$resid)