emacs ess apply function to token under point

Question

I've finally committed to moving over to both emacs and ess -- and i'm having a bit of trouble getting (the famously customisable) combination to work as i'd like.

Say that i have a file that contains an object called rainfall open in emacs and an inferior R session open. Is there a way that i can put point over the token and then send it to the R process for a function to be applied to that object?

To make it concrete, say the source file contains the following object:

rainfall <- xts(runif(100, min = 0, max = 10), seq.Date(as.Date('2019-01-01'), by = 1, length = 100))

I'd like to be able to put point anywhere inside the token rainfall and (via some keyboard shortcut) send it to the R process with some function (such as head, tail, plot, or summary) applied to it.

So in the iESS[R] screen i'd see: R> tail(rainfall) and the associated output.

Answer 1

You can achieve what you want quickly with a keyboard macro for each Emacs session.

But it looks like you would want to have several standard functions available to quickly examine R objects, so it will be more flexible to do it in Emacs Lisp.

(require 'ess-r-mode)
(defun r-summary-at-point ()
  (interactive)
  (let ((sym (ess-symbol-at-point)))
    (if sym
        (ess-send-string (get-buffer-process "*R*") 
                         (concat "summary(" (symbol-name sym) ")\n") t)
      (message "No valid R symbol at point"))))

(define-key ess-r-mode-map (kbd "C-c :") 'r-summary-at-point)

That function does not check to make sure the "*R*" process buffer exists, but will work once you have started the process, assuming the default.