# topic 7i:  Scatter plots
     #  first generate the data to use in the plot
source("../gnrnd4.R")
gnrnd4(1273370910, 450008500425)
     #  This generated both L1 and L2.
     #  L1 holds the x values
L1
     #  L2 holds the coresponding y values
L2
     #  then all we need to do is to use the 
     #  plot function to get a graph
plot( L1, L2 )
     #  add some horizontal and vertical lines
     #  at the tick marks
abline( h=seq(30,55,5),   # from 30 to 55 in steps of 5
        v=seq(35,55,5),   # from 35 to 55 in steps of 5
        lty="dotted",     # use dotted lines
        col="blue")       # make them blue lines
     #  That is sufficient for the requirements
     #  of this course, but, as usual, it would
     #  be nice to really fix up the plot
plot( L1, L2,
      main="Scatter Plot", # adds a title
      xlab="x values",     # specifies the x axis label
      ylab="y values",     # specifies the y axis label
      xlim=c(30,60),       # sets x to go from 30 to 60
      ylim=c(20,60),       # sets y to go from 20 to 60
      xaxp=c(30,60,15),    # sets 15 spaces between x
                           #    tick marks from 30 to 60
      yaxp=c(20,60,20),    # sets 20 spaces between y
                           #    tick marks from 20 to 60
      las=1,               # sets axis values to horizontal
      pch=19,              # sets the points to be 
                           #    large filled dots
      col="red")           # sets the color of the dots
                           # to be red
abline( h=seq(20,60,2), v=seq(30,60,2),
        col="blue", lty="dotted")
abline( h=seq(20,60,10), v=seq(30,60,10),
        col="darkblue", lty="dashed")
#
# Here are the EPA values of carbon monoxide levels
#    measured at various dates at on location (values
#    are in parts per million)

CO <- c( 0.35, 0.636, 0.554,  0.343, 
         0.842, 0.219, 0.1375, 0.375)
# Here are the EPA values for nitrogen dioxide levels
#    measured at the same location on the same days
#    (values are in parts per billion)
NO2 <- c(6.26, 17.08, 14.85, 8.44, 
         19.37, 5.78, 3.1, 8.73)
#  get a scatter plot of that data
plot( CO, NO2, 
      main="Data from the EPA",
      xlab="CO (in ppm)",
      ylab="NO2 (in ppb)")
abline( h=seq(5,20,5), v=seq(0.2, 0.8, 0.1),
        lty="dashed", col="darkgray")
#
# Then, we will go back and enter the dates
#     of the measurements so that we can get a line
#     chart
epa_dates <- as.Date( c( "2019-01-08", "2019-01-16",
                         "2019-01-17", "2019-01-23",
                         "2019-01-27", "2019-01-29",
                         "2019-02-08", "2019-02-22"))
    # first we can do this as a scatter plot
plot( epa_dates, CO)
    # then fix this up with the x-axis values
plot( epa_dates, CO, xaxt="n", xlab="",
      ylim=c(0,1), yaxp=c(0,1,10), las=1,
      ylab="Carbon Monoxide (ppm)",
      main="Data from the EPA")
axis.Date(side = 1, dd, format = "%m/%d/%Y", 
          las=2, at=epa_dates, cex.axis=0.6)
abline(v=epa_dates, h=seq(0,1,0.1), 
       col="blue", lty="dotted")
#  then, by using the type= parameter we can get a line
#  plot
plot( epa_dates, CO, 
      type="l", xaxt="n", xlab="",
      ylim=c(0,1), yaxp=c(0,1,10), las=1, col="red",
      pch=16,
      ylab="Carbon Monoxide (ppm)",
      main="Data from the EPA")
axis.Date(side = 1, dd, format = "%m/%d/%Y", 
          las=2, at=epa_dates, cex.axis=0.6)
abline(v=epa_dates, h=seq(0,1,0.1), 
       col="blue", lty="dotted")
#
     #  but we may want to fix this up with all the
     #  dates on the x axis.  And while we are 
     #  doing than let us make this plot show
     #  both points and connecting lines
plot( epa_dates, CO, 
      type="b", xaxt="n", xlab="",
      ylim=c(0,1), yaxp=c(0,1,10), las=1, col="red",
      pch=16,
      ylab="Carbon Monoxide (ppm)",
      main="Data from the EPA")
axis.Date(side = 1, dd, format = "%m/%d/%Y", 
          las=2, at=seq(as.Date("2019-01-08"),
                        as.Date("2019-02-22"), 1),
          cex.axis=0.6)
abline(v=epa_dates, h=seq(0,1,0.1), 
       col="blue", lty="dotted")