#+TITLE: Testing the :post header arg

# Set some Org Babel values for the whole document
#+PROPERTY: header-args:R :session *myR*

* Introduction
  In this document I explore the use of the =:post= header argument
  for Org mode source code blocks. My aim is to create several tables
  for export to LaTeX and have the =ATTR_LATEX= blocks automatically
  added to the output of the source code blocks.

  For these tests we wil use the =mtcars= data set that comes with R.

* Testing the =:post= header argument
  The following block is supposed to be used in a =:post= call to set
  the =ATTR_LATEX= line.
  #+name: attr_wrap
  #+begin_src R :var data="" :results output
  cat("#+ATTR_LATEX: :environment tabularx  :width \\textwidth :align Xrrr", "\n")
  data
  #+end_src

  The idea is to use this as a named src block so it can be reused for
  each table I want to create (here still without =:post= to show the
  regular output).
  #+name: create_table
  #+begin_src R :rownames yes :colnames yes :var brand="Mazda"
  mtcars[grepl(brand, rownames(mtcars)), c("mpg", "cyl", "disp")]
  #+end_src

  This works using =#+call:=:
  #+call: create_table(brand="Hornet")

  #+RESULTS:
  |                   |  mpg | cyl | disp |
  |-------------------+------+-----+------|
  | Hornet 4 Drive    | 21.4 |   6 |  258 |
  | Hornet Sportabout | 18.7 |   8 |  360 |

  Define a slightly different src block that actually uses the =:post=
  header argument:
  #+name: create_table2
  #+begin_src R :rownames yes :colnames yes :var brand="Mazda" :post attr_wrap(data=*this*)
  mtcars[grepl(brand, rownames(mtcars)), c("mpg", "cyl", "disp")]
  #+end_src

  And call it:
  #+call: create_table2(brand="Toyota")

  #+RESULTS:
  : #+ATTR_LATEX: :environment tabularx  :width \textwidth :align Xrrr
  :                X  mpg cyl  disp
  : 1 Toyota Corolla 33.9   4  71.1
  : 2  Toyota Corona 21.5   4 120.1

  Note that the whole results block is preceded by a colon, instead
  of being formatted by Org.

  Using the Shell code from the Org manual doesn't work either, it
  adds a comma in front of the =#+ATTR_LATEX= line.
  #+name: attr_wrap2
  #+begin_src sh :var data="" :results output
    echo "#+ATTR_LATEX: :environment tabularx :width \\textwidth :align Xrrr"
    echo "$data"
  #+end_src

  New =create_table= function:
  #+name: create_table3
  #+begin_src R :rownames yes :colnames yes :var brand="Mazda" :post attr_wrap2(data=*this*)
  mtcars[grepl(brand, rownames(mtcars)), c("mpg", "cyl", "disp")]
  #+end_src

  And call it:
  #+call: create_table3(brand="Toyota")

  #+RESULTS:
  : #+ATTR_LATEX: :environment tabularx :width \textwidth :align Xrrr
  : Toyota Corolla	33.9	4	71.1
  : Toyota Corona	21.5	4	120.1

  Observe that now the column names have completely disappeared.