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Date: Tue, 21 Sep 2010 20:25:46 +0100
From: Ian Hobson <ian@ianhobson.co.uk>
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To: user@couchdb.apache.org
Subject: Re: Random Document
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On 21/09/2010 18:27, Peter Braden wrote:
> Hi,
>
> Is there a good way to get a random document from a database.
Hmm, that depends upon what you mean by "good", and "random" and if you 
want a repeatable result! I guess I'm asking what exactly are you trying 
to do?

a) Pick a representative, and statistically defensible sample of size X 
from a population of Y documents where each document has an equal 
probability of being selected, and cannot be selected twice.

b) Take a sample of size 1 from a population of Y, X times (so a given 
document could be taken more than once)?

c) Something similar to a or b where you don't know Y in advance?

d) Shuffle the documents?

  I'm currently
> using a view that does:
>
> function(doc) {
>      emit(Math.random(), doc);
> };
>
> But as this isn't deterministic, I'm pretty sure it's wrong.
I don't follow your logic. The view will show all documents in a random 
order. The fact that is is unrepeatable may make it useless for your 
purposes, but it does not make the maths invalid, or the statistics wrong.

Regards

Ian