How to sort an index file in lucene

Question

I have an index which made by lucene and each document in it have 3 filed that one of them is a numeric field which is my frequency. I search in my index but before it I want to sort it by the numeric field. is there any way to sort it by lucene before my search?

Answer 1

Sorting before searching doesn't really make a lot of sense, since Lucene is creating an inverted index for searching against, rather than storing and searching through a sequential set of documents.

However, it sounds like you want to run a search and get results that are already sorted in a specified way.

This is done by passing a Sort to the IndexSearcher.search call, like:

SortField field = new SortField("frequency", SortField.Type.FLOAT);
//Sorting, first, by "frequency", then by relevance score
Sort sort = new Sort(field, Sort.FIELD_SCORE);
searcher.search(query, maxDocs, sort);

The name of the field makes me wonder if you aren't re-inventing the wheel though. Lucene already factors term frequency into it's relevance scores. If you want to tweak that sort of scoring, if might be a better idea to create a custom Similarity class to calculate scores for you, extending either TFIDFSimilarity or DefaultSimilarity, and overriding the method tf, particularly.