The examples here are created using R 2.6.2 for Windows XP. It uses the standard graphics package that R loads automatically when it starts.
The examples use hsb2 data set that can be downloaded as follows.
hsb2 < read.table('http://www.ats.ucla.edu/stat/r/modules/hsb2.csv', header=T, sep=",") attach(hsb2)
plot(math, write) 

plot(math, write) abline(lsfit(write, math)) #alternatively plot(math, write) fit<lm(write ~ math) abline(fit) 

# pch for plotting characters, or symbol to use # see help(points) for more information on pch for hsb2_female<hsb2[female==1,] hsb2_male<hsb2[female==0,] with(hsb2_female, plot(math, write, pch=20, col="darkred")) with(hsb2_male, points(math, write, pch=22, col="darkblue")) # alternatively math_male<hsb2$math[female==0] write_male<hsb2$write[female==0] math_female<hsb2$math[female==1] write_female<hsb2$write[female==1] plot(math_female, write_female, type="p", pch=20, col="darkred") points(math_male, write_male, pch=22, col="darkblue")


# adding legend hsb2_female<hsb2[female==1,] hsb2_male<hsb2[female==0,] with(hsb2_female, plot(math, write, pch=20, col="darkred", ylim=c(25, 70))) with(hsb2_male, points(math, write, pch=22, col="darkblue")) legend(65, 35, c("female", "male"), pch=c(20, 22), cex=.8, col=c("darkred", "darkblue"))


math_male<hsb2$math[female==0] write_male<hsb2$write[female==0] math_female<hsb2$math[female==1] write_female<hsb2$write[female==1] plot(math_female, write_female, type="p", pch=20, col="darkred", ylim=c(25, 70)) points(math_male, write_male, pch=22, col="darkblue") abline(lsfit(write_female, math_female), col="darkred") abline(lsfit(write_male, math_male), col="darkblue") legend(65, 35, c("female", "male"), pch=c(20, 22), cex=.8, col=c("darkred", "darkblue"))

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