Adding Lines to a Plot
# 15.3a Basic lines ====================================================== 15.3a
myV1 = c(1, 2, 4, 5, 8) # Some data to work with
myV2 = c(1.5, 3, 2, 7, 6)
png(filename = "illustrations/fig-15-8-lines-BW.png",
units = "in", # Set measurements in inches
res = 1200, # Set resolution at 1200dpi
width = 6, # Width at 6 inches
height = 4) # Height at 4 inches
par(mar = c(4.2, 4, 1, 1)) # Set margin widths in lines
plot(myV1, myV2, # A simple default scatterplot
pch = 19, col = "darkgray", # Solid point markers in darkgray
xlim = c(0, 10), ylim = c(0, 10)) # Set range for x & y axes
# Line 1 - a horizontal dashed line
abline(h = 1.5, # Add a horizontal line at y = 1.5
lwd = 3, # Give it a width of 3
lty = 2, # Dash it all
col = gray(.4)) # Make it medium gray
text(x = 8, y = 2.2, # Add label for line 1
label = "Line 1", # Label text
cex = 2, # Set size to 2
col = gray(.4)) # Set color to gray .4
# Line 2 - a vertical line with long dashes
abline(v = 4, # Add a vertical line at x = 4
lwd = 8, # Give it a width of 8
lty = "longdash", # Use long dashes
col = gray(.7)) # Make it light gray
text(x = 3.5, y = 6, # Add label for line 2
label = "Line 2", # Label text
cex = 2, # Set size to 2
srt = 90, # Rotate text to vertical
col = gray(.7)) # Set color to light gray
# Line 3 - abline using coefficients
abline(a = 3.2, # Add a line w/ intercept = 3.2
b = 1.5, # and slope = 1.5
lwd = .5, # Give it a width of .5
col = gray(.2)) # Make it dark gray
text(x = 1.5, y = 6.5, # Add label for line 3
label = "Line 3", # Label text
cex = 2, # Set size to 2
srt = 44, # Rotate text
col = gray(.2)) # Set color to dark gray
# Line 4 - Line segment
lines(x = c(6, 12), # x values for line segment
y = c(11, 4), # y values for line segment
lty = 4, # Dot-dash pattern
col = gray(.1), # Make it dark gray
lwd = 2, # Set line width at 2
xpd = TRUE) # Allow outside plot area
text(x = 8, y = 9.75, # Add label for line 4
label = "Line 4", # Label text
cex = 2, # Set size to 2
srt = -34, # Rotate text
col = gray(.1), # Set color to dark gray
xpd = TRUE) # Allow to extend beyond plot
# Line 5 - A regression line
myReg = lm(myV2 ~ myV1) # A simple regression model
abline(reg = myReg, # Use regression model to define line
col = "black") # Set color
text(x = 6, y = 6, # Add label for line 5
label = "Line 5", # Label text
cex = 2, # Set size to 2
srt = 23, # Rotate text
col = "black") # Set color
dev.off() # Output the png file