# Movies Example -- source code file movies.r

# Read and print data frame.
movies = read.table("movies2.txt", header=T)
cat("movies data frame:\n")
print(movies)

# Create new data frame using dummy variables.
star_dum = as.numeric(movies$isstar == "Star")
sum_dum = as.numeric(movies$issum == "Summer")
with_dummy_vars = data.frame(title=movies$title,
	                           opening=movies$opening,
	                           budget=movies$budget,
                             star_dum=star_dum,
                             sum_dum=sum_dum)
cat("with_dummy_vars data frame:\n")
print(with_dummy_vars)

# Perform backward selection to pick best model.
fullmodel = lm(opening ~ budget + star_dum + sum_dum, 
             data=with_dummy_vars)
print(summary(step(fullmodel, direction="backward")))

# Obtain best model after looking at step summary.
model = lm(opening ~ budget + star_dum, data=with_dummy_vars)

# Create scatterplots and residual plots.
r = residuals(model)
p = fitted(model)
attach(with_dummy_vars)
pdf("movies.pdf")

# Plot A
plot(budget, opening, 
   main="Plot A: Scatterplot Using Plotting Symbol star_dum",
   xlab="Movie Budget",
   ylab="Opening Weekend Gross",
   pch=as.character(star_dum))

# Plot B
plot(budget, opening, 
   main="Plot B: Scatterplot Using Plotting Symbol sum_dum",
   xlab="Movie Budget",
   ylab="Opening Weekend Gross",	
   pch=as.character(sum_dum))

# Plot C
plot(p, r, 
   main="Plot C: Residual Plot Using Plotting Symbol star_dum",
   xlab="Predicted Values",
   ylab="Residuals",
   pch=as.character(star_dum))
   abline(h=0, lty="dashed", col="red")
   
# Plot D
plot(budget, r, 
   main="Plot D: Residual Plot Using Plotting Symbol star_dum",
   xlab="Movie Budget",
   ylab="Residuals",
   pch=as.character(star_dum))
   abline(h=0, lty="dashed", col="red")
   
# Plot E  This plot is not very useful, but it shows how
# to plot residuals vs. a dummy variable.
plot(sum_dum, r, 
   main="Plot E: Residual Plot Using Plotting Symbol star_dum",
   xlab="Dummy Variable for issummer",
   ylab="Residuals",
   pch=as.character(star_dum))
   abline(h=0, lty="dashed", col="red")
   
dev.off( )