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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.

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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.

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  • I tried this code, but got the error Symbol's value as variable is void: ess-r-mode-map. – ricardo May 18 '20 at 0:14
  • Sorry - I know why - I will edit my answer. You need to require the library first. – gregoryg May 18 '20 at 0:51
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    for some reason ess-r-mode-map broke things (even if i required it above); the good news is that this works (define-key ess-mode-map (kbd "C-c :") 'r-summary-at-point). this is probably another question, but if you have an opinion on ess-r-mode-map v. ess-mode-map i'm interested (or some links!). – ricardo May 18 '20 at 1:40
  • ess-mode-map is more general, and probably better to use - but it's been a couple years since I used ESS on a daily basis, so take that with a grain of salt. The important thing is that you can call the function and it works - the key binding is another matter. You can always run functions with M-x eval-expression or ` a quick M-: - always try that before using a key combo! You probably already know that :-) – gregoryg May 18 '20 at 3:53
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    I've asked a related question -- i'm building up a lot of boilerplate code in my .emacs file so i'm trying to figure out how to create a general function so that i can declare on of these in a single line. – ricardo May 18 '20 at 5:31

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