my-external-r-code.R

# ---- set-up-the-data

# Set up some sample data 
xvars <- -10:10 
yvars <- xvars^2 

# ---- print-the-data

# Display the xvars 
# Note that I don't really want to 
# display the xvars, 
# but this line is included 
# to demonstrate that text output 
# won't show up in the RMarkdown 
# in this example. 

xvars 

# ---- print-the-data-with-print

print(yvars) 

# ---- plot-the-data

# Create the plot 
plot(xvars, yvars) 
points(xvars, yvars, pch = 16, col = "red", cex = 1.5)