Show only specific representative point using ggplot2

Question

This question is quite basic about ggplot2, but I could not find the answer elsewhere.

I want to have a line graph(built from all the data) and to add points only for specific cases.

Example:

x= seq(1:10)
y = 2*x
df = data.frame(x,y)
ggplot(df,aes(x,y))+geom_line()

Now I would like to emphasise some of the date by points, for example all the y points which can be divided without remainder by 6.

Answer 1

Like this?

library(ggplot2)
x  <- seq(1:10)
y  <- 2*x
df <-  data.frame(x,y)
ggplot(df,aes(x,y))+
  geom_line()+ 
  geom_point(data=df[df$y%%6==0,],size=5,colour="red")