rm(list=ls())

# remove variables from previous session
rm(list=ls())

# read file
dfr <- read.csv(file="FCAT_Mult_grade3.csv",head=TRUE,sep=",") 

#ssrss03 = FCAT Reading Score
#Orfwrcf = Oral Reading Fluency – FCAT Passages

print(dfr$ssrss03)
print(dfr$Orfwrcf)
regr = lm(ssrss03 ~ Orfwrcf, data=dfr)
plot(dfr$ssrss03, dfr$Orfwrcf)

#create artificial data
# objective: the line y = .4 x + 2

nb.pts = 50
x = sample(seq(-5,5,.01), nb.pts)
y = .4*x + 2

#---------------------------------
par(mfrow=c(2,2))
fluct = c(.05,.25,.5,2.5)
y1 = y+rnorm(nb.pts, sd=fluct[1])
y2 = y+rnorm(nb.pts, sd=fluct[2])
y3 = y+rnorm(nb.pts, sd=fluct[3])
y4 = y+rnorm(nb.pts, sd=fluct[4])

c1 = cor(x,y1); c1 = paste(c("cor= ", c1))
c2 = cor(x,y2); c2 = paste(c("cor= ", c2))
c3 = cor(x,y3); c3 = paste(c("cor= ", c3))
c4 = cor(x,y4); c4 = paste(c("cor= ", c4))

plot(x,y1,main=c1); plot(x,y2,main=c2) 
plot(x,y3,main=c3); plot(x,y4,main=c4)
#----------------------------------
par(mfrow=c(1,1))