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From Dennis Berger <>
Subject ranking / scoring by field which contains a given rank?
Date Tue, 20 Feb 2007 12:57:48 GMT
Hi List,
is it possible to sort or rank by a specific field which contains only 
integer numbers? I have a few million products with a specific salesrank.
If somebody searches "palm", he will get thousands of items, pocket 
adapter, pens everything else but not the most selled items. Which are 
not accessoires, but the main palm handheld. I would like that he got it 
sorted by salesrank. And it would be nice if this could be done while 
indexing. Is this possible?
If not, are there alternatives?

Right now I fetch 2000 items and sort them by hand and kick 1900 
products away to get the best 100 items. But thats a bad idea since you 
always have to fetch a lot more items than you actually need to get 
proper results..
So I had an idea an implemented the following:

I have to say that I concat all textfields "articleno, description, long 
description" to one fulltext field.
I parse the salesrank of each item, and calculate a boost factor by 
using and logarithmic interpolation with two given points.
x0/f0 = 1/5000 and x2/f2 = 250,1.
That Way I can get very high numbers for the best selled items. Linear 
boosting shouldn't be enough.
Now I set this boostfactor on the fulltext field and after that I add 
the field and add the document.
One should expect that searching a common item, you should get the best 
selled first.
But my tests showed that it doesn't matter how I set my x0/f0 x1/f1 the 
results are nearly the same bad results.
First item is salesrank 238 second is salesrank 36.
If you take this example I boosted the fulltext field of the item with 
salesrank 36 with a factor of 1510.
salesrank 238 was only boostet with a factor of 1,507. (this is german 
notation for the decimal number one dot five. NOT one thousand five 
I wonder why boosting one item with a factor of thousand and one with a 
factor of ONE doesn't make a difference?
The search term appeared 2 to 3 times on each item.
I tried values between 100000 and 1. even setting boost evertime to 1, 
gives me the quite same results. With exactly the same first 20 items.

I'm stuck, maybe you can help.

My code follows.

 public float calcBoostinterpolLog(int x){
        if(x > 1000)
                return 0.001F;
        double result;
        int x0 = 1;
        int f0 = 50000;
        int x1 = 250;
        int f1 = 1;

        result = f0 * Math.exp(  ((x - x0)*(Math.log(f1) - Math.log(f0)) 
) / (x1 -x0));
        return new Float(result);

 Field field_fulltext = new 
Field(Messages.getString("Indexer.FieldFulltext"), fulltext, 

kinda regards,

Dennis Berger
Eduardstrasse 43b
20257 Hamburg

Phone: +49 (0)40 54 00 18 17
Mobile: +49 (0) 179 123 15 09

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