Click to get scatter plot coordinates

Question

Say I'm making a scatter chart with thousands of points:

ggplot(head(data, n=2000), aes(length, coverage))+ geom_point(alpha = 0.5, color = 'navyblue') + coord_trans(x='log', y='log') 

alt text http://fourmidable.unil.ch/temp/scatterplot.png

I want to add the labels “20 or so of the most extreme points” (in the upper right and lower right corners). They are easy to identify visually. But getting them programmatically seems a bit of a burden. (many if statements are required).

Is there any way to click on the graphical output R to get their exact coordinates?

Thanks, Yannick

Answer 1

The grid analog (ggplot2 package, as well as the lattice package is based on the grid graph) of the locator () - grid.locator ().

Thanks Book of Deepayan of the Sarkar Lattice !

Answer 2

I don't know with ggplot , but with basic graphics you can use identify :

 plot(length,coverage,type='p') identify(length,coverage) 

Now you can use the mouse to click on the points, and R will show which observation they correspond. Pressing a mouse button other than the first completes the process, and identify returns the case numbers as a value.