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From Matt Quail <>
Subject Iterating TermEnum backwards
Date Thu, 26 Feb 2004 06:42:47 GMT
Hi all,

Is there any way to iterate through a TermEnum backwards? Okay, I know
that there isn't a way to do this via the TermEnum class, but is it
"implementable" on top of the underlying Lucene datastore?

My particular problem is this:

I have an index of documents, each document has a "date" field (I'm
using DateField). Most documents have a different date, so the number of
unique dates is close to the number of documents.

I want to find the top N most recent dates, but I don't want to have to
iterate through ALL of them first. NB: With DateField, the earlier dates
are lexocographically smaller. (I also want to find the most recent N
less than some date D).

I know I could "invert" my dates (something like MAX_LONG - date) to get
the REVERSE order, but I want to be able to do "least recent" and "most

Is iterating over a TermEnum "impossible", or should I dig further, and
possibly submit a patch?


PS: my current solution is to do a binary search between MIN and MAX,
halving my search space until I find close to N matching documents.

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