# ------------------------------------------------
# Program: Univariate3.S  
#  Author: Steven M. Boker
#    Date: Thu Sep 23 12:46:53 EST 2004
#
# Provides examples of the use of QQ plots for the 
# visualization of univariate distributions
#
# ------------------------------------------------

# ------------------------------------------------
# Quantile plot of sepal length using the "plot" command. 

graphsheet(height=6.4,width=6.4)
tLength <- length(iris$sepal.length)
plot(c(1:tLength)/tLength, sort(iris$sepal.length),
         xlab = "Fraction Value",
         ylab="Sepal Length (cm)")

# ------------------------------------------------
# Quantile plot of sepal length using Trellis graphics 

graphsheet(height=6.4,width=6.4)
qqmath(~ sepal.length, 
         distribution=qunif, data=iris,
         aspect=1,
         xlab = "Fraction Value",
         ylab="Sepal Length (cm)")

# ------------------------------------------------
# Quantile plot of sepal length conditioned by variety

graphsheet(height=4,width=7.5)
qqmath(~ sepal.length | variety,
         distribution=qunif,
         data=iris,
         panel = function(x, y) {
           panel.grid()		
           panel.xyplot(x, y)
         },
         layout=c(3,1), 
         aspect=1,
         xlab = "Fraction Value",
         ylab="Sepal Length (cm)")


# ------------------------------------------------
# Quantile-Normal plot of sepal length against normal distribution 

graphsheet(height=6.4,width=6.4)
qqnorm(iris$sepal.length, 
        xlab = "Quantiles from Normal Distribution", 
        ylab = "Quantiles from Sample")


# ------------------------------------------------
# Quantile-Quantile plot of sepal.length against normal distribution 

graphsheet(height=6.4,width=6.4)
qqmath(~ sepal.length, 
         distribution=qnorm, data=iris,
         prepanel = prepanel.qqmathline, 
	 panel = function(x, y) {
	   panel.qqmathline(y, distribution = qnorm)
	   panel.qqmath(x, y)
	 },
         aspect=1,
         xlab = "Normal Distribution",
         ylab="Sepal Length (cm)")

# ------------------------------------------------
# Quantile-Quantile plot of sepal.length against normal distribution
# by the conditioning variable variety. 

graphsheet(height=6.4,width=6.4)
qqmath(~ sepal.length | variety, 
         distribution=qnorm, data=iris,
         prepanel = prepanel.qqmathline, 
	 panel = function(x, y) {
	   panel.qqmathline(y, distribution = qnorm)
	   panel.qqmath(x, y)
	 },
         aspect=1,layout=c(2,2),
         xlab = "Normal Distribution",
         ylab="Sepal Length (cm)")

# ------------------------------------------------
# Quantile-Quantile plot of sepal.length of Setosa versus Versicolor 

graphsheet(height=6.4,width=6.4)
qq(variety ~ sepal.length, 
         data=iris,
         subset=variety=="Setosa" | variety=="Versicolor",
         aspect=1)