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Date: Tue, 28 Jul 2009 20:46:01 -0700
Message-ID: <7db9abd30907282046m1221d370k3bd68ea3b963f87f@mail.gmail.com>
Subject: Re: Chaining MapReduce function pairs
From: kowsik <kowsik@gmail.com>
To: user@couchdb.apache.org
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It doesn't have to be a separate DB though. Example would be: you want
to run a view (report), say once a day, and then trend on this (using
another view).

It's possible to generate the view results, add that back to couchdb
as a document with a timestamp and then have meta-views that
map/reduce these views to pull out trends and what not. I've done this
and works like a charm. This kinda view is awesome from a motion chart
perspective (http://code.google.com/apis/visualization/documentation/gallery/motionchart.html)
where you can see 4-dimensional data transforming (time being one of
the dimensions).

While couch doesn't "natively" support this, this kind of thing is
possible since the results of a view is just JSON which itself can be
another native document.

K.

On Tue, Jul 28, 2009 at 8:00 PM, Paul Joseph
Davis<paul.joseph.davis@gmail.com> wrote:
> There's nothing builtin. Me and a couple others have tried to do such things
> but nothing has ever stuck. At the moment your best bet would be to write
> som helpers to copy view output to a new db and go from there.
>
>
>
> On Jul 28, 2009, at 4:53 PM, Cortland Klein <me@pixelcort.com> wrote:
>
>> I'm interested in creating views that chain multiple pairs of MapReduce
>> functions together. This would allow me, for example, to do complex data
>> analysis that's not possible with only one pair of MapReduce functions.
>> When I say chain I mean the second map function takes as its input the
>> key-value pairs outputted by the first reduce functions.
>>
>> Is this something CouchDB can do or will be able to do in the future?
>>
>> --
>> Cortland Klein <me@pixelcort.com> +1 408 506 9791
>> http://pixelcort.com/
>> 2260 California Street #13
>> Mountain View, CA, USA 94040
>