[Exist-open] purge an index file data size

[ㄏ. <dn...@gm...>]

Dear list-members,

Is it possible to purge an index of obsolete entries after an xml collection
has been substantially pruned?

I have a 10gb n-gram index file, which was created by indexing 4,000 xml
files.  I have since removed 2,000 files from the collection, and would like
to avoid re-indexing the remaining half.  Is there a way I can clear the old
index data without deleting the entire index and starting again?

If anyone has any suggestions, I would be very grateful to hear them.