How to plot the grand median in the given plot?



I am currently trying to plot a plot between age and the friend the have for this I have created a bucket of 4 to know how many friend people will have depended upon the year joined to social networking site.

ggplot(aes(x = age, y = friend_count),data = subset(pf, ! + geom_line(aes(color = year_joined.bucket), stat = 'summary', fun.y = median)

I want to know how to plot the Grand median from each bucket to know which bucket is close to the Grand Median.


Do you notice any problem with the data?

Why does the friend count rise noticeably after age 80? Can you find the reason, and cleanup the data as needed? Perhaps the seniors have superfast free internet and free training?

Here is a solution for adding the grand median: