SID-02074: Construction of hash with list elements

Status:	Answered	TWiki version:	6.0.0	Perl version:
Category:	SpreadSheetPlugin	Server OS:	Ubuntu Linux 14.01	Last update:	10 years ago

This question is extends my previous question where I wanted to display the table containing

format="|$formfield(paper_title) | $formfield(conference) | $percntFORMFIELD{ \"deadline_abstract\" topic=\"$formfield(conference)\" }$percnt |"

became the hint to use hashes to make the retrieval more efficient. This works perfect!

Now I want to provide the inverse view to the "conference - paper" relation.
In particular, I want to generate a table of upcoming conferences, and provide a list of papers submitted to each of them.
Using hashes, I thought it might be efficient to scan the list of conference papers and incrementally construct a hash called

map_conf2paper

in the mimics of $SETMHASH function. Assuming that there is a list papers and conferences and a hash mapping

map_papers2conf

associating each paper with the corresponding conference I want to construct a mapping one-to-many mapping between conferences and papers.

%CALCULATE{
  $SETLIST(swallow_comma,
    $LISTEACH(
      $SETMHASH(map_conf2paper, $GETHASH(map_papers2conf, $item), +$item),
      $GETLIST(papers)
    )
  )
}%

I am using $SETMHASH as a placeholder to indicated the required cumulation of values associated with a single hash key. I tried to use $INSERTSTRING and access the hash map_conf2paper within the $LISTEACH to incrementally append to a string values, but apparently the hash variable constructed using $SETHASH is available only when the variable finished the job. Many thanks for a hint in advance.

-- Rostislav Chudoba - 2015-06-18

Discussion and Answer

You can't use $SETMHASH in your case; as you noticed it only works with numbers. Here is a working solution with example:

%CALCULATE{
  $LIST2HASH(p2c, p10, c1, p11, c1, p12, c1, p12, c2, p12, c3, p20, c2, p21, c2, p30, c3, p31, c3)
  $SETLIST(tmp, 
    $LISTEACH(
      $SET(c, $GETHASH(p2c, $item))
      $SETHASH(
        c2p,
        $GET(c),
        $item $GETHASH(c2p, $GET(c))
      ),
      $GETHASH(p2c)
    )
  )
  $GETHASH(c2p, c3)

This example returns papers p31 p30 p12 for conference c3. The papers are concatenated by space: $item $GETHASH(c2p, $GET(c)); you could concatenate with comma-space, but then you get a trailing empty list item, which you can strip using $LISTNONEMPTY() when you retrieve a hash element containing a list of papers.

-- Peter Thoeny - 2015-06-23

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