From: Gerd Stolpmann <info@gerd-stolpmann.de>
To: Ian Zimmerman <itz@buug.org>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Hashtbl or Set?
Date: Tue, 20 Sep 2011 12:13:07 +0200 [thread overview]
Message-ID: <1316513587.16477.11.camel@thinkpad> (raw)
In-Reply-To: <87sjnsl2f0.fsf@foolinux.dyndns.org>
Am Montag, den 19.09.2011, 13:09 -0700 schrieb Ian Zimmerman:
> I need a somewhat large (thousands) set of strings, created once during
> startup and never modified after. What is a better choice, a (string,
> unit) Hashtbl.t or the Set module? If the Set module still uses trees
> as it did when I was young :-), access will be logarithmic versus
> constant for Hashtbl. But on the other hand a hash function must
> examine all of every string while the comparison of 2 strings stops at
> the first nonmatching character.
>
> I am thinking about the time to build the set as well as the probing
> time.
Nothing has changed so far. Besides naive Hashtbl and Set you have at
least two more options: Hashtbl with self-defined hash function (i.e.
one that stops after the n-th char), and Set with a hash-based
comparison function (i.e. compare first the hashes of the strings, and
only if the hashes are equal, compare the strings).
In my experience, for a large constant set a Hashtbl usually works best.
Set is usually only better when you can profit from functional updates.
Gerd
>
> --
> Ian Zimmerman
> gpg public key: 1024D/C6FF61AD
> fingerprint: 66DC D68F 5C1B 4D71 2EE5 BD03 8A00 786C C6FF 61AD
> Rule 420: All persons more than eight miles high to leave the court.
>
--
------------------------------------------------------------
Gerd Stolpmann, Darmstadt, Germany gerd@gerd-stolpmann.de
Creator of GODI and camlcity.org.
Contact details: http://www.camlcity.org/contact.html
Company homepage: http://www.gerd-stolpmann.de
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*** programming in Ocaml? Gerd Stolpmann can help you.
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prev parent reply other threads:[~2011-09-20 10:13 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-19 20:09 Ian Zimmerman
2011-09-19 20:17 ` Basile Starynkevitch
2011-09-20 10:13 ` Gerd Stolpmann [this message]
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