# R help for the topic 13 assignment

1. How do I compute a least-squares fit, residuals, and predicted values?

The basic syntax is

fit=lm(response~predictor)

This won't print anything, but you can get different summaries as follows.

fit

  gives the intercept and slope

fit$residuals

  is a vector of residuals

fit$fitted

  is a vector of fitted values

abline(fit)

  adds the least-squares fit to the current graph

2.  Standardized residuals?

Assuming that you already have stored the least-squares fit in the 
variable fit ...

rstandard(fit)
   
  compares standardized residuals

3. How do I do a scatterplot with different symbols or colors?

In the homework, you wish to plot Miles against TravTime with different
symbols for the different directions.

TravDir (the direction) is coded -2, -1, 0, 1, 2

If you want to plot with different symbols for direction ...

plot(Miles, TravTime, pch=TravDir+3)

Or if you wish to use different colors ..

plot(Miles, TravTime, col=TravDir+3)

Actually, I prefer solid dots ...

plot(Miles, TravTime, col=TravDir+3, pch=19)

Should also add a legend ...

legend("topleft",legend=c("West","Somewhat West","North/South",
  "Somewhat East","East"),
  col=1:5,pch=19)