r - Different colours in ggplot based on geom_smooth -

i created ggplot linear geom_smooth have points, geom_point have different colour below , above linear smooth line.

i know can add color point doing geom_point(aes(x, y, colour = z)). problem how determine if point in plot below or above linear line.

can ggplot2 or have create new column in data frame first?

below sample code geom_smooth without different colours above , below line.

any appreciated.

library(ggplot2)  df <-  data.frame(x = rnorm(100),               y = rnorm(100))  ggplot(df, aes(x,y)) +  geom_point() +  geom_smooth(method = "lm") 

i believe ggplot2 can't you. say, create new variable in df make colouring. can so, based on residuals of linear model.

for example:

library(ggplot2)  set.seed(2015) df <-  data.frame(x = rnorm(100),                   y = rnorm(100))  # fit linear regression l = lm(y ~ x, data = df)  # make new group variable based on residuals df$group = na df$group[which(l$residuals >= 0)] = "above" df$group[which(l$residuals < 0)] = "below"  # make plot ggplot(df, aes(x,y)) +   geom_point(aes(colour = group)) +   geom_smooth(method = "lm") 

note colour argument has passed geom_point(), otherwise geom_smooth() produce fit each group separately.

result: