From: Friedrich Dominicus <frido@q-software-solutions.com>
Subject: Re: alist and multiple values for one key
Date: 20 Jan 2003 17:03:09 +0100 [thread overview]
Message-ID: <877kcz6c76.fsf@fbigm.here> (raw)
In-Reply-To: dafb954c.0301200503.2118ecf9@posting.google.com
ncauderan@hotmail.com (Norbert C.) writes:
> 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)
That does not work this way. assoc can only be used with a symbol but
if you step into the list you just have other lists.
This code will work for the given data:
(defun collect-if (pred list)
(mapcar #'(lambda (el) (when (funcall pred el) el)) list))
you can call it with
(collect-if #'(lambda (item) (eq (car item) 'pine)) trees)
((pine . cones) (pine . acorns))
Regards
Friedrich
next prev parent reply other threads:[~2003-01-20 16:03 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-01-20 13:03 alist and multiple values for one key Norbert C.
2003-01-20 16:03 ` Friedrich Dominicus [this message]
2003-01-20 23:53 ` Hannu Koivisto
2003-01-21 6:30 ` Friedrich Dominicus
2003-01-21 6:57 ` Friedrich Dominicus
2003-01-20 16:07 ` Klaus Berndl
2003-01-20 17:18 ` Kai Großjohann
2003-01-20 17:19 ` Kai Großjohann
2003-01-20 23:45 ` Hannu Koivisto
2003-01-21 10:53 ` Oliver Scholz
2003-01-21 11:04 ` David Kastrup
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