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From kowsik <>
Subject Re: Chaining MapReduce function pairs
Date Wed, 29 Jul 2009 03:46:01 GMT
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 (
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.


On Tue, Jul 28, 2009 at 8:00 PM, Paul Joseph
Davis<> 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 <> 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 <> +1 408 506 9791
>> 2260 California Street #13
>> Mountain View, CA, USA 94040

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