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From Toke Eskildsen>
Subject Re: Sorting on mutivalued fields still impossible?
Date Wed, 05 Sep 2012 07:54:36 GMT
On Fri, 2012-08-31 at 13:35 +0200, Erick Erickson wrote:
> Imagine you have two entries, aardvark and emu in your
> multiValued field. How should that document sort relative to
> another doc with camel and zebra? Any heuristic
> you apply will be wrong for someone else....

I see two obvious choices here:

1) Sort by the value that is ordered first by the comparator function.
Doc1: aardvark, (emu)
Doc2: camel, (zebra)
This is what Uwe wants to do and it is normally done by preprocessing
and collapsing to a single value.
It could be implemented with an ordered multi-valued field cache by
comparing on the first (or last, in the case of reverse sort) entry for
each matching document.

2) Make duplicate entries in the result set, one for each value.
Doc1: aardvark, (emu)
Doc2: camel, (zebra)
Doc1: (aardvark), emu
Doc2: (camel), zebra
I have a hard time coming up with a real world use case for this.
It could be implemented by using a multi-valued field cache as above and
putting the same document ID into the sliding window sorter once for
each field value.

Collapsing this into a single algorithm:
Step through all IDs. For each ID, give access to the list of field
values and provide a callback for adding one or more (value, ID)-pairs
to the sliding windows sorter. 

Are there some other realistic heuristics that I have missed?

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