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From David Birtwell <>
Subject Re: Alphabetical sorting of results
Date Thu, 31 Oct 2002 14:53:47 GMT

There is a technique for predifining an ordering of results at index 
time that might be applicable here.  It involves making slight 
modifications to the Lucene source.  Here's a summary from another mail 
I had written on the subject:

I was faced with a similar problem.  We wanted to have a numeric rank 
field in each document influence the order in which the documents were 
returned by lucene.  While investigating a solution for this, I wanted 
to see if I could implement strict sorting based on this numeric value. 
I was able to accomplish this using document boosting, but not without 
modifying the lucene source.  Our "ranking" field is an integer value 
from one to one hundred.  I'm not sure if this will help you, but I'll 
include a summary of what I did.

In DocumentWriter remove the normalization by field length:
   float norm = fieldBoosts[n] * 
   float norm = fieldBoosts[n];

In TermScorer and PhraseScorer, modify the score() method to ignore the 
lucene base score:
   score *= Similarity.decodeNorm(norms[d]);
   score = Similarity.decodeNorm(norms[d]);

In, make byteToFloat() public.

At index time, use Similarity.byteToFloat() to determine your boost 
value as in the following pseudocode:
   Document d = new Document();
   ... add your fields ...
   int rank = d.getField("RANK"); (range of rank can be 0 to 255)
   float sortVal = Similarity.byteToFloat(rank)

In your situation, perhaps you could define a rank based on the 
alphabetic ordering value of your title field.  With only 256 discreet 
boost values currently available to you, though, you'll probably have to 
group your titles alphabetically into buckets.

You also might want to investigate modifying the lucene source to return 
the same score for each hit, then index your files in alphabetical 
order.  I *believe* that, independent of score, lucene will return the 
results in the order in which they were indexed.


Eoin O'Toole wrote:

> I am indexing documents (about 7 different document types) and must 
> display the results alphabetically by title field... which is 
> generally not one of the search fields.
> Currently I am calling hits.get(i) on each document to find the title, 
> and then sorting by title. Sort is fast, but calling hits.get(i)  n 
> times is too slow beyond about 400 objects... and this approach means 
> I have to do a "full scan" of the Hits collection.
> Anyone have any suggestions/strategies on solving this? (Or is there 
> functionality already in place I have overlooked?)
> Thanks for any input,
> Eoin
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