Elasticsearch filter based on field similarity

Question

For reference, I'm using Elasticsearch 6.4.0

I have a Elasticsearch query that returns a certain number of hits, and I'm trying to remove hits with text field values that are too similar. My query is:

{
  "size": 10,
  "collapse": {
    "field": "author_id"
  },
  "query": {
    "function_score": {
      "boost_mode": "replace",
      "score_mode": "avg",
      "functions": [
        {
          //my custom query function
        }
      ],
      "query": {
        "bool": {
          "must_not": [
            {
              "term": {
                "author_id": MY_ID
              }
            }
          ]
        }
      }
    }
  },
   "aggs": {
    "book_name_sample": {
      "sampler": {
        "shard_size": 10
      },
      "aggs": {
        "frequent_words": {
          "significant_text": {
            "field": "book_name",
            "filter_duplicate_text": true
          }
        }
      }
    }
  }
}

This query uses a custom function score combined with a filter to return books a person might like (that they haven't authored). Thing is, for some people, it returns books with names that are very similar (i.e. The Life of George Washington, Good Times with George Washington, Who was George Washington), and I'd like the hits to have a more diverse set of names.

I'm using a bucket_selector to aggregate the hits based on text similarity, and the query gives me something like:

...,
"aggregations": {
        "book_name_sample": {
            "doc_count": 10,
            "frequent_words": {
                "doc_count": 10,
                "bg_count": 482626,
                "buckets": [
                    {
                        "key": "George",
                        "doc_count": 3,
                        "score": 17.278715785140975,
                        "bg_count": 9718
                    },
                    {
                        "key": "Washington",
                        "doc_count": 3,
                        "score": 15.312204414323656,
                        "bg_count": 10919
                    }
                ]
            }
        }
    }

Is it possible to filter the returned documents based on this aggregation result within Elasticsearch? IE remove hits with book_name_sample doc_count less than X? I know I can do this in PHP or whatever language uses the hits, but I'd like to keep it within ES. I've tried using a bucket_selector aggregator like so:

"book_name_bucket_filter": {
                    "bucket_selector": {
                        "buckets_path": {
                          "freqWords": "frequent_words"
                        },
                        "script": "params.freqWords < 3"
                    }
                }

But then I get an error: org.elasticsearch.search.aggregations.bucket.sampler.InternalSampler cannot be cast to org.elasticsearch.search.aggregations.InternalMultiBucketAggregation

Also, if that filter removes enough documents so that the hit count is less than the requested size, is it possible to tell ES to go fetch the next top scoring hits so that hits count is filled out?

Answer 1

Why not use top hits inside the aggregation to get relevant document that match the bucket? You can specify how many relevant top hits you want inside the top hits aggregation. So basically this will give you a certain number of documents for each bucket.