Range filter for count of documents with the same value for a field - elasticsearch

Question

In my index my-books, each document represents a book and has a field authorId, which uniquely represents the author of the book. I want to run a search query with a range filter on the total number of books authored by the book's author.
For example: say, if I have four authors A, B, C, D.
A is the author for books a1, a2,a3.
B is the author for book b1.
C is the author for books c1,c2.
D is the author for books d1, d2, d3, d4.
Lets say I want to retrieve all books such as the number of books written by the same author is greater than 1 but less than 4. Then my result hits are [a1, a2, a3, c1, c2].
How do I write such a query?

Answer 1

You need to use
terms aggregation to group by authors
top_hits to get documents under that author
bucket_selector to get terms where doc count is less than 4
{
"aggs": {
"NAME": {
"terms": {
"field": "author.keyword",
"size": 10
},
"aggs": {
"books": {
"top_hits": {
"size": 10
}
},
"final_filter": {
"bucket_selector": {
"buckets_path": {
"values": "_count"
},
"script": "params.values < 4"
}
}
}
}
}
}
Result
"aggregations" : {
"NAME" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : "A",
"doc_count" : 2,
"books" : {
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "index148",
"_type" : "_doc",
"_id" : "-_pOUHoBVZyA6L_G1XrM",
"_score" : 1.0,
"_source" : {
"book" : "a1",
"author" : "A"
}
},
{
"_index" : "index148",
"_type" : "_doc",
"_id" : "_PpPUHoBVZyA6L_GL3q5",
"_score" : 1.0,
"_source" : {
"book" : "a3",
"author" : "A"
}
}
]
}
}
},
{
"key" : "B",
"doc_count" : 1,
"books" : {
"hits" : {
"total" : {
"value" : 1,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "index148",
"_type" : "_doc",
"_id" : "_fpPUHoBVZyA6L_GWHpg",
"_score" : 1.0,
"_source" : {
"book" : "b1",
"author" : "B"
}
}
]
}
}
},
{
"key" : "C",
"doc_count" : 1,
"books" : {
"hits" : {
"total" : {
"value" : 1,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "index148",
"_type" : "_doc",
"_id" : "_vpPUHoBVZyA6L_Gmnoj",
"_score" : 1.0,
"_source" : {
"book" : "c1",
"author" : "C"
}
}
]
}
}
}
]
}
}