Regression line for the entire dataset together with regression lines based on groups in R ggplot2 ?

Question

I am new to ggplot2 and have problem displaying the regression line for the entire data-set together with the regression lines for groups. So far i can plot regression line based on the group but I have no success in getting the regression line for the entire data-set on the same plot. I want all the regression lines with different line style so that they can be easily identified in black and white print. Any help would be highly appreciated. here is my code so far:

ggplot(alldata,aes(y = y, x = x, colour= group, shape= group )) +
geom_point(size = 3, alpha = .8) + geom_smooth(method="lm", fill=NA , size = 1) 

Answer 1

Try placing the colour, shape, linetype aesthetics not in the original call to ggplot2

You can then add the overall line with a different colour

set.seed(1)
library(plyr)
alldata <- ddply(data.frame(group = letters[1:5], x = rnorm(50)), 'group', 
                 mutate, y=runif(1,-1,1) * x +rnorm(10))



ggplot(alldata,aes(y = y, x = x)) +
     geom_point(aes(colour= group, shape= group), size = 3, alpha = .8) + 
     geom_smooth(method="lm", se= F, size = 1, aes(linetype = group, group = group)) +
     geom_smooth(method = 'lm',size = 1, colour = 'black', se = F) + theme_bw()