From: Friedrich Dominicus <frido@q-software-solutions.com>
Subject: Re: alist and multiple values for one key
Date: 21 Jan 2003 07:30:12 +0100 [thread overview]
Message-ID: <87n0lvf217.fsf@fbigm.here> (raw)
In-Reply-To: 87iswjv0mh.fsf@lynx.ionific.com
Hannu Koivisto <azure@iki.fi> writes:
> Friedrich Dominicus <frido@q-software-solutions.com> writes:
>
> > 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))
>
> I'm afraid that is not what your example expression evaluates to.
> Did you try it?
Yes I tried it. I can not see why mapcan should be used here. I'm
consing up a list if the predicate function yields true. So mapcar is
the right choice.
What I originally wanted was:
(defun find-all-matching (pred list)
(delete-if #'(lambda (item) (not (funcall pred item))) list))
but that won't work with Emacs Lisp but this will:
(defun find-all-matching (pred list)
(delete-if `(lambda (item) (not (,pred item))) list))
So I suggest you tell me why mapcar is not the proper
function to use.
Regards
Friedrich
> Learn about mapcan
if you want to get your code
> right using one of the map... functions. Of course, to return
> just the values as requested by the OP you will need other changes
> as well.
>
> --
> Hannu
next prev parent reply other threads:[~2003-01-21 6:30 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
2003-01-20 23:53 ` Hannu Koivisto
2003-01-21 6:30 ` Friedrich Dominicus [this message]
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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