unset an org-babel property?

Question

In org-mode, if I set the :file header-arg at some point, like all header args, it is inherited at lower levels. I want to avoid duplicating the header-arg all over. In the case of :session, the special value none is used to not associate the code block with any existing session, it s always a new session. I want the special value for :file, which represents do not write this to a file, but insert it directly as usual.

* set at top header level
  :PROPERTIES:
  :header-args: :R :file "abcd.pdf" :exports both :results output graphics
  :END:

#+BEGIN_SRC R 
x = seq( from = -2, to = 2, by = 0.1)
plot (x,x^2,col="red", type="l")
#+END_SRC

** lower level header 
# output still goes to abcd.pdf, but I don't want it to, I want it inserted
#+BEGIN_SRC R 
2 + 2
#+END_SRC

Answer 1

It looks like you can override the PROPERTY default values on a block-by-block basis:

* CONFIG
#+PROPERTY: header-args:R :session *R* :results output 

* TESTING
  #+name: data-setup-silently
  #+begin_src R :results silent
    x <- 1:10
  #+end_src

  #+name: results-silently
  #+begin_src R :results silent
     print(x)
  #+end_src

  #+name: results
  #+begin_src R 
     print(x)
  #+end_src

Here:

• The PROPERTY sets the default :results to output
• Block 1: set up the data, and override with silent to shut up about it
• Block 2: print out the results, but override with silent to prevent results from being added to the buffer
• Block 3: default behavior: print out the results to the buffer

Answer 2

My solution to this problem is to set up yasnippets with a few different header arguments. It works well as long as you only have a few different options and use only 1 or 2 languages.