Mailing-List: contact user-help@couchdb.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@couchdb.apache.org
Received-SPF: pass (nike.apache.org: domain of kevin@meebo-inc.com designates
 64.78.22.18 as permitted sender)
From: Kevin Ferguson <kevin@meebo-inc.com>
To: "user@couchdb.apache.org" <user@couchdb.apache.org>
Date: Wed, 26 Aug 2009 15:46:39 -0700
Subject: RE: Looking for help/ideas on how to fetch a Rank from a CouchDB
 based 	Highscores system
Thread-Topic: Looking for help/ideas on how to fetch a Rank from a CouchDB
 based 	Highscores system
Thread-Index: AcomnYC9p2ZcybC7QmGeUSF2o7lc/wAAZIVV
Message-ID: 
 <CE1513D67312104D86366A5A25E2B1EC14CC5C61E9@EXVMBX017-12.exch017.msoutlookonline.net>
References: <9ce8c9f70908261418s5807965ax2b9e23a0578dcff8@mail.gmail.com>
In-Reply-To: <9ce8c9f70908261418s5807965ax2b9e23a0578dcff8@mail.gmail.com>
Accept-Language: en-US
Content-Language: en-US
acceptlanguage: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

If I understand you right, I would try this:

map:
emit(doc.score, 1)

reduce: return sum(v);

When you query on a particular key, you get the number of docs with that ex=
act score.

When you query on a range, you get the number of docs with scores in that r=
ange.  So to find the rank of e.g. score 25, you could query startkey=3D26&=
endkey=3D99999999, which will return the number of docs that have 26 or hig=
her.

hth

Kevin
________________________________________
From: larryroot@gmail.com [larryroot@gmail.com] On Behalf Of Larry [contact=
@lroot.com]
Sent: Wednesday, August 26, 2009 2:18 PM
To: user@couchdb.apache.org
Subject: Looking for help/ideas on how to fetch a Rank from a CouchDB based=
     Highscores system

I currently have a a bunch of "high score" documents in couchdb. I'm trying
to find the best way for me to create a view that would allow me to easily
get the rank for a given score. As an example consider that I have 5 high
scores:

1) John, 100 pts
2) Jane, 90 pts
3) Bill, 85 pts
4) Jen, 70 pts
5) Bob, 55 pts

I have a function in my application called getRank( int $score) which would
return the rank (int) for the given score. So for example, using the scores
above:

getRank(30) =3D=3D 6
getRank(71) =3D=3D 4
getRank(101) =3D=3D 1

My document structure for a highscore is:

{
   "_id": "0a68cdbe4a8d130662217f3abf4046bc",
   "_rev": "1-1264504508",
   "score": "000000000000000000000000000000100",
   "player_name": "John"
}

My initial approach was to create a view that does emit([doc._id,doc.score]=
,
null). I Then query the view by setting my start key to the *top* of the
view list and set my end key to the value of the score I'm looking for. I
then count the results that are returned and derive the rank that way. This
is grossly inefficient I know and I'm having a hard time trying to find the
most optimal way to construct this. Any thoughts are ideas would be greatly
appreciated.

Thanks

larry