Re: exporting nested list to CSV file

[Christopher Howard <cmhoward2@alaska.edu>]

On Tue, 22 Jul 2014 21:35:35 +0200
Thorsten Jolitz <tjolitz@gmail.com> wrote:

> Christopher Howard <cmhoward2@alaska.edu> writes:
> 
> > Hi. I've been using the pcsv library to parse data from external CSV
> > files, then using various elisp functions to filter/munge the
> > data. Afterwards, I was sad to discover that pcsv does not have any
> > functions for /writing/ data back to a CSV file.
> >
> > Since the data is well-structured, presumably this shouldn't be hard
> > to do. Could I get some guidance on what would be the simplest
> > approach? Is there another library I've overlooked? Or some
> > built-ins that would be especially helpful? The data are in lists
> > like so:
> >
> > (("row0datastring", "row0datastring", "row0datastring", ...)
> >  ("row1datastring", "row1datastring", "row1datastring", ...)
> >  ...
> > )
> 
> try something like:
> 
> #+begin_src emacs-lisp 
>   (mapconcat
>    'identity
>    (append
>     '("row0datastring" "row0datastring" "row0datastring")
>     '("row1datastring" "row1datastring" "row1datastring")) ",")
> #+end_src
> 
> #+results:
> :
> row0datastring,row0datastring,row0datastring,row1datastring,row1datastring,row1datastring
> 

Thank you for helping me get started. I also needed to address the
issues of 1) newlines at the end of rows and 2) character escaping. To
address the second issue, I used "prin1", which I hope is a good
enough hack for my purposes:

#+begin_src emacs-lisp
(defun to-csv-row (fields)
  (mapconcat 'prin1-to-string fields ","))

(defun to-csv-string (nested-list)
  (mapconcat 'to-csv-row nested-list "\n"))

(defun to-csv-file (path nested-list)
  "Converts NESTED-LIST to csv format and exports to file. NESTED-LIST is
   expected to be the structure provided by the pcsv library."
  (with-temp-file path
    (insert (to-csv-string nested-list))))
#+end_src