modify default org babel default headers

Question

I would like to have more control on the R session in org-mode so that I only have to chage the session name in one place for the modification to affect the whole buffer. The only way I could think this through was to modify the org-babel-default-header-args.

I want to define a function so that I can modify the default arguments easily. But I don't know how to pass the name of the session as a string. see the code below.

(defun set-session-name (&optional r-session-name r-session-directory)
  (interactive (list
                (read-from-minibuffer "r-session-name: " "*R*" )
        (read-from-minibuffer "r-session-directory: " "/home/test/")))  
  (setq org-babel-default-header-args:R
    (cons '(:dir . "%s" r-session-directory))
    (cons '(:session . r-session-name) 
          (assq-delete-all :session org-babel-default-header-args:R))
          ))

(:dir . "%s" ression directory "/home/test/") is obviously wrong. Can you help please?

** Some details ** Let's say that we are in an .org buffer and I have a buffer wide header like the following. With the session name being remote-R-remote* and the ouput being silenced :output silent

 #+PROPERTY: header-args:R :session *remote-R-remote*  :exports results :colnames yes :results output silent :output-dir images/ :dir "/ssh:gnu:/home/livelygnu/Documents/R/" :eval yes :cache yes

* Some First steps

    #+Name: 
    #+BEGIN_SRC R 
    do some stuffs
    #+END_SRC

Now if in a subtree we want to produce a certain number of graphs but don't want to write :results output graphics all the time along with the file extension we have to redefine the whole header argument for this subtree.

** output some graphs
:PROPERTIES:
:header-args:R: :session *remote-R-remote* :results output graphics :output-dir: images/ :eval yes :file-ext pdf
:END:

    #+Name: name_of_graphs
    #+BEGIN_SRC R 
    plot(a)
    #+END_SRC

    many more graphs possibly

We can do the same for latex output for example

** output some results
:PROPERTIES:
:header-args:R: :session *remote-R-remote* :results output latex :output-dir: 
:END:


#+Name: name_of_graphs
#+BEGIN_SRC R 
output latex block
#+END_SRC

Now let's say while our estimation is working on the session remote-R-remote (possibly a long computation), we want to continue to work on some graphs in another session. for that we would have to change the :session names for all the code block that we need. But If instead we modify the default arguments in org-babel-default-header-args. Then changing the key :session there would change the session everywhere. Of course this mean that we would not have to write :session *remote-R-remote* all the time as well since we can put it as default.

Answer 1

I'd apply the buffer wide property syntax (org-mode 9), e.g. for an R (session) buffer called *R*:

#+PROPERTY: header-args:R :session *R*

org-mode <9:

#+PROPERTY: session *R*

And do C-c C-c on this line to activate new settings.