R dummies

You also can use the function abline() to create a sloped line through yourplot. In fact, by specifying the arguments a and b, you can draw a line that fitsthe mathematical equation y = a + b*x. In other words, if you specify thecoefficients of your regression model as the arguments a and b, you get a linethrough the data that is identical to your prediction line:> abline(a=coef(fit)[1], b=coef(fit)[2])Even better, you can simply pass the lm object to abline() to draw the linedirectly. (This works because there is a method abline.lm().) This makes yourcode very easy:> abline(fit, col = “red”)Different plot typesThe plot function has a type argument that controls the type of plot that getsdrawn. For example, to create a plot with lines between data points, use type=”l”;to plot only the points, use type=”p”; and to draw both lines and points, usetype=”b”:> plot(LakeHuron, type=”l”, main=’type=”l”’)> plot(LakeHuron, type=”p”, main=’type=p”’)> plot(LakeHuron, type=”b”, main=’type=”b”’)Your resulting graphics should look similar to the three plots in Figure 16-5.The plot with lines only is on the left, the plot with points is in the middle, and theplot with both lines and points is on the right.Using R functions to create more types of plotAside from plot(), which gives you tremendous flexibility in creating yourown plots, R also provides a variety of functions to make specific types ofplots. (You use some of these in Chapters 14 and 15). Here are a few toexplore:Scatterplot: If you pass two numeric vectors as arguments to plot(),the result is a scatterplot. Try:> with(mtcars, plot(mpg, disp))