Term stats script score POC

[afoucret]

A proof of concept of term stats query.

Add documentFrequencyStatistics and termFrequencyStatistics helpers to the painless script_score query so it can be used to build term stats based query.

To be continued to add additional stats (total term frequency, term positions).

##Example:##

1. Add few docs:

PUT /movies/_doc/1
{ "title": "star wars"}

PUT /movies/_doc/2
{
  "title": "star trek"
}

PUT /movies/_doc/3
{ "title": "rambo"}

2. Test the documentFrequencyStatistics helper:

GET /_search
{
  "query": {
    "script_score": {
      "query": { "match_all": {} },
      "script": {
        "source": "return documentFrequencyStatistics(\"title\", \"star wars story\").getMin()"        
      }
    }
  }
}

Output:

{
  "took": 5,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 3,
      "relation": "eq"
    },
    "max_score": 2,
    "hits": [
      {
        "_index": "movies",
        "_id": "2",
        "_score": 2,
        "_source": {
          "title": "star trek"
        }
      },
      {
        "_index": "movies",
        "_id": "1",
        "_score": 2,
        "_source": {
          "title": "star wars"
        }
      },
      {
        "_index": "movies",
        "_id": "3",
        "_score": 2,
        "_source": {
          "title": "rambo"
        }
      }
    ]
  }
}

3. Test the termFrequencyStatistics helper:

GET /_search
{
  "query": {
    "script_score": {
      "query": { "match_all": {} },
      "script": {
        "source": "return termFrequencyStatistics(\"title\", \"star wars\").getSum()"        
      }
    }
  }
}

{
  "took": 8,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 3,
      "relation": "eq"
    },
    "max_score": 2,
    "hits": [
      {
        "_index": "movies",
        "_id": "1",
        "_score": 2,
        "_source": {
          "title": "star wars"
        }
      },
      {
        "_index": "movies",
        "_id": "2",
        "_score": 1,
        "_source": {
          "title": "star trek"
        }
      },
      {
        "_index": "movies",
        "_id": "3",
        "_score": 0,
        "_source": {
          "title": "rambo"
        }
      }
    ]
  }
}