#########################################################
# Hamster Example: source code file hamster-matrix.txt  #
# Compute XtX, Xty, XtX inverse, yty.                   #
#########################################################

# Read and print data frame.
hamster = read.table("c:/datasets/hamster.txt", header=T)
cat("hamster data frame\n")
print(hamster)

# Obtain X and y matrices.
# Obtain number of observations n.
n = nrow(hamster)
cat("\nNumber of observations: ", n, \n")

y = matrix(hamster$Lifetime, n, 1, byrow=T)
cat("\ny: \n")
print(y)

X = cbind(rep(1, n), hamster$Hiber)
cat("\nX:\n")
print(X)

xtx = t(X) %*% X
cat("\nXtX:\n")
print(xtx)

xty = t(X) %*% y
cat("\nXty:\n")
print(xty)

cat("\nXtX inverse:\n")
print(solve(xtx))

yty = t(y) %*% y
cat("\nyty:\n")
print(yty)