Rank feature field type

A rank_feature field can index numbers so that they can later be used to boost documents in queries with a rank_feature query.

  1. PUT my-index-000001
  2. {
  3.   "mappings": {
  4.     "properties": {
  5.       "pagerank": {
  6.         "type": "rank_feature" 
  7.       },
  8.       "url_length": {
  9.         "type": "rank_feature",
  10.         "positive_score_impact": false 
  11.       }
  12.     }
  13.   }
  14. }
  16. PUT my-index-000001/_doc/1
  17. {
  18.   "pagerank": 8,
  19.   "url_length": 22
  20. }
  22. GET my-index-000001/_search
  23. {
  24.   "query": {
  25.     "rank_feature": {
  26.       "field": "pagerank"
  27.     }
  28.   }
  29. }

Rank feature fields must use the rank_feature field type

Rank features that correlate negatively with the score need to declare it

rank_feature fields only support single-valued fields and strictly positive values. Multi-valued fields and negative values will be rejected.

rank_feature fields do not support querying, sorting or aggregating. They may only be used within rank_feature queries.

rank_feature fields only preserve 9 significant bits for the precision, which translates to a relative error of about 0.4%.

Rank features that correlate negatively with the score should set positive_score_impact to false (defaults to true). This will be used by the rank_feature query to modify the scoring formula in such a way that the score decreases with the value of the feature instead of increasing. For instance in web search, the url length is a commonly used feature which correlates negatively with scores.