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Re: alist and multiple values for one key
From: |
Klaus Berndl |
Subject: |
Re: alist and multiple values for one key |
Date: |
Mon, 20 Jan 2003 17:07:01 +0100 |
On 20 Jan 2003, Norbert C. wrote:
> Hi,
>
> I would lile to find the "good way" to retrieve multiple
values
> for a given key in an alist.
>
> But I didn't find a natural way to do it. For example :
> (setq trees '((pine . cones) (pine . acorns) (oak . acorns) (maple .
> seeds)))
> ==> ((pine . cones) (pine . acorns) (oak . acorns) (maple . seeds))
> (assoc 'pine trees)
> ==> (pine . cones)
>
> What I'd like is something that returns each value associated with
> 'pine.
>
> Any thought ?
Multimaps are unfortunately not build in in Emacs. But you can implement
it
very easy. Here is a first fast hack how you can do it, probably not
robust
and fancy enough but it gives you a first impression:
,----
| ;; a fast hack for a multimap
| (defvar multimap nil)
|
| (defun multimap-add (key value)
| (let ((elem (assoc key multimap)))
| (if elem
| (when (not (member value (cdr elem)))
| (setcdr elem (append (list value) (cdr elem))))
| (setq multimap (cons (list key value) multimap)))
| multimap))
|
| (defun multimap-get (key)
| (interactive "sKey: ")
| (message "%s" (cdr (assoc key multimap))))
|
|
| ;; some tests
| (multimap-add "key1" "value1-1")
| (multimap-add "key1" "value1-2")
| (multimap-add "key2" "value2-1")
| (multimap-add "key2" "value2-2")
| (multimap-add "key2" "value2-3")
| (multimap-add "key3" "value3-3")
`----
Klaus
--
Klaus Berndl mailto: klaus.berndl@sdm.de
sd&m AG http://www.sdm.de
software design & management
Thomas-Dehler-Str. 27, 81737 München, Germany
Tel +49 89 63812-392, Fax -220