mtcars2 <- mtcars mtcars2$trans <- factor(mtcars$am, levels=0:1, labels=c("automatic", "manual")) mtcars2$gear <- as.factor(mtcars$gear) mtcars2$am <- NULL mtcars2$vs <- NULL mtcars2$drat <- NULL mtcars2$carb <- NULL mtcars2$wt <- NULL mtcars2$hp <- NULL mtcars2$qsec <- NULL p <- ggplot(mtcars2) print( p + geom_point(aes(x=disp, y=mpg, shape=trans)) + scale_shape_manual(values=c(1, 3)) ) print( ggplot(mtcars2, aes(x=disp, y=mpg)) + geom_point() + stat_smooth(aes(group=trans), method="lm") )