Question about using :cache in Babel (for R)

[Michael Hannon <jm_hannon@yahoo.com>]

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Greetings.  I have a question that relates to the use of the :cache option in
Babel sessions using R.

Here's the relevant configuration information:

    Emacs  : GNU Emacs 23.2.1 (x86_64-redhat-linux-gnu, GTK+ Version 2.24.4)
     of 2011-05-23 on x86-12.phx2.fedoraproject.org
    Package: Org-mode version 7.7 (release_7.7.328.g1a97)

I've appended the text of a file that exhibits the issue, which is the
following.  If I explicitly evaluate a given code block, using, let's say, C-c
C-c, I get the results stuck into the Org file, as in the first source-code
block below.  If I then repeatedly export the file (to PDF, HTML, etc.), I get
the cached results in the exported document.  For instance, the mean of the
random variable does not change as I repeatedly export the file.

If for some reason I have NOT explicitly evaluated a given code block, as with
the second code block below, then during export I see a message "Evaluating
code block" (or similar), indicating that Babel is NOT using a cached version,
and no cacheable output is produced as a result, meaning that the entire
calculation will be repeated during the next export.  For instance, the mean
of the random variable will be different every time I export the file.

I guess I can see the logic of this, but I wonder if there is some way to
instruct Babel to automatically cache the output of any code blocks it
evaluates, i.e., via a header argument or elisp variable or ... .

Thanks,

-- Mike

P.S. Is the SHA1(?) identifier for the results a new feature?

----------

#+TITLE: 
#+AUTHOR:
#+DATE:

#+STARTUP: hideblocks
#+BABEL: :session *R* :cache yes :results output verbatim :exports both
:tangle yes

* This is a test

#+begin_src R

  x = rnorm(10)
  mean(x)

#+end_src

#+results[9b9372488662083d0d211b9aad9c2985faba20cd]:
: [1] -0.07904561

* Here's a second test

#+begin_src R

  x = rnorm (50)
  summary(x)

#+end_src

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