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Date: Fri, 8 Jan 2010 09:51:51 -0800
Message-ID: <e282921e1001080951n1d299934u57170e937062a1@mail.gmail.com>
Subject: Re: Ordering results from reduce function
From: Chris Anderson <jchris@apache.org>
To: user@couchdb.apache.org
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On Fri, Jan 8, 2010 at 6:10 AM, Borja Mart=EDn <borjam@dagi3d.net> wrote:
> Hi,
> suppose I have the typical view used to index the tags of a document:
>
> // map
> function(doc) {
> =A0for (var idx in doc.tags) {
> =A0 emit(doc.tags[idx], 1);
> =A0}
> }
>
> // and then I have this reduce function to count how many documents I hav=
e
> for each given tag:
> function(key,values) {
> =A0return sum(values);
> }
>
> and with the following sample documents:
> { "tags" : ["foo", "foo bar"] },
> { "tags" : ["foo", "bar", "foo bar"]}
>
> I get these results:
> {"rows":[
> =A0{"key":"bar","value":1},
> =A0{"key":"foo","value":3},
> =A0{"key":"foo bar","value":2}
> ]}
>
> What I want to do is to get the results ordered by its value so I can kno=
w
> which are the most used tags for example. I know that the results are
> ordered by the key so I guess this could be done if I could use the value
> returned by the reduce on it while calling the emit function with somethi=
ng
> like emit([reduce_value, tag], null); Is there any way to accomplish that=
?
>

This is a common request, but not supported directly by CouchDB's
views -- to do this you'll need to copy the group-reduce query to
another database, and build a view to sort by value.

This is a tradeoff we make in favor of dynamic range queries and
incremental indexes.

Chris

> Has it sense or am I misunderstanding something?
>
> Thanks in advance
>
> Regards
>
> --
> def dagi3d(me)
> =A0case me
> =A0 when :web then =A0"http://dagi3d.net"
> =A0 when :twitter then "http://twitter.com/dagi3d"
> =A0end
> end
>


--=20
Chris Anderson
http://jchrisa.net
http://couch.io