I found this post that provides a nice function for conveniently showing some information about R objects in ESS mode. ESS already shows some information about functions as you type them (in the status bar) but this has wider scope. Move the point over an R object (a function, a data frame, etc), hit C-c C-g and a tooltip pops up showing some relevant information about the object, such as the arguments a function takes or a basic summary for a vector and so on. As written it’s a little unwieldy to use it on large dataframes, but it would be easy to modify the function used to summarize a particular class of object. Here’s the code:

There’s also a quick screencast of it in action:

Pretty handy. I’ve incorporated this into the Emacs Starter Kit.