When we create a plot, it shows the values passed by the function for creating the plot but we might want to display some other values to provide some information through the plot and that information could be a threshold value as a horizontal line or we can also call it a cut off value. This can be done by using geom_hline function of ggplot2 package.
Consider the below data frame −
> x<-rnorm(20) > y<-rnorm(20,1.5) > df<-data.frame(x,y) > df
x y 1 0.27810573 2.6545571 2 1.39185082 3.4845292 3 -0.19068920 1.7043852 4 1.00791317 1.4324814 5 -1.74964913 1.7996093 6 -0.13123079 2.5004350 7 0.15729145 2.6425085 8 0.42815918 -0.2970325 9 -0.84252471 0.2579510 10 0.25413824 3.0670546 11 -0.05608811 1.6974104 12 -0.85671276 0.8638574 13 -1.17183043 2.5650640 14 2.67224782 0.4832468 15 -0.01763065 3.3835275 16 1.26122484 1.1755709 17 1.91652453 1.6351443 18 0.82211772 0.9123337 19 -0.19153555 0.1831160 20 0.31878745 3.1280550
Creating a scatterplot between x and y −
> library(ggplot2) > ggplot(df,aes(x,y))+geom_point()
Adding a horizontal line in the above plot −
> ggplot(df,aes(x,y))+geom_point()+geom_hline(yintercept=0.5)