[Haskell-beginners] Creating Indexes

[Carl Eyeinsky]

Hi, Martin

try ixset [0].

But as you said, a simple data structure is not enough for your use case,
as any "mere" data structure has some concrete performance characteristics.
Something more abstract is needed.


[0] http://hackage.haskell.org/package/ixset

On Mon, Dec 15, 2014 at 7:20 AM, martin <martin.drautzburg at web.de> wrote:
>
> Am 12/14/2014 04:41 PM, schrieb Christopher Reichert:
> >
> > On Sun, Dec 14 2014, martin <martin.drautzburg at web.de> wrote:
> >> Hello all,
> >>
> >> I recently wrote a Haskell program, which accesses Lists extensivly.
> That was okay to verify the overall idea, but
> >> performance degraded rapidly when I made the lists bigger. There was a
> quadratic effect and this was not surprizing,
> >> given the nature of the code.
> >>
> >
> > Are you certain this was because of the List and not something else?
> >
> > If you are constantly doing lookups on lists then, indeed, performance
> > will suffer.
> >
> >> I am somewhat aware of Haskell types which offer faster access. But
> they all seem to assume that I know the way data is
> >> accessed when I write the type. A new access path may force me to
> rededign the type.
> >>
> >> What I am looking for is something which behaves like indexes in a
> RDBMS, i.e. to define a list-like type on an innocent
> >> data type (like a tuple) and then add indexes as needed. Is there such
> a thing?
> >
> >
> > Would an association list fit the model you are talking about?
>
>
> Well I *have* an association list, however with more than one column by
> which I lookup rows (relationally spreaking). I
> know I can use Maps, but I cannot convert to a map for every lookup,
> because it will be more expensive than just
> taversing the list.
>
> I can also just use Maps all along, but this requires I settle for one key
> column (or a combination of columns). When
> the necessity arises to lookup by new criteria (other columns) I would
> have to redesign the map or add another map or
> whatever. In any case it is very different to adding an index in a RDBMS.
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-- 
Carl Eyeinsky
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