Average and histogram aggregation on nested fields in elasticsearch

Question

I have a nested document in elasticsearch like this:

{
  {
  "doctxt": "doca",
    "nested": [
      {
        "pos": 1,
        "txt": "terma"
      },
      {
        "pos": 2,
        "txt": "termb"
      },
      {
        "pos": 3,
        "txt": "termc"
      }
    ]
  },
  {
  "doctxt": "docb",
    "nested": [
      {
        "pos": 1,
        "txt": "termd"
      },
      {
        "pos": 2,
        "txt": "terma"
      },
      {
        "pos": 3,
        "txt": "termb"
      }
    ]
  }
}

Aggregation queries that do work:

Total count for a specific term (match_all query, aggregation on term txt), result:

terma: 2
termb: 2
termc: 1
termd: 1

Facets on txt field for a specific term (filter on term txt, aggregation on term txt), results:

terma: termb (2), termc (1), termd (1)
termb: terma (2), termc (1), termd (1)
termc: terma (1), termb (1)
termd: terma (1), termb (1)

What I can't do with this document is following:

Average pos for a specific term (I end up getting the average on the whole nested positions, in this case always 2 for any term), expected results:

terma: 1.5
termb: 2.5
termc: 3
termd: 1

Histogram for a specific term (not working for the same reason as above), expected results:

terma: pos 1 (1), pos 2 (1)
termb: pos 2 (1), pos 3 (1)
termc: pos 3 (1)
termd: pos 1 (1)

If I have flat documents (doca-1-terma, doca-2-termb, doca-3-termc, docb-1-termd, ...) I get the expected results. Is this a limit in aggregating nested documents and should I store the data in twice in a flat format and in the current nested format?

vaidik vaidik · Accepted Answer · 2014-07-21T07:46:18

No not really. You can achieve what you need to achieve with nested types. Nested types will make your nested data treat individually and get your expected results.

Try this Gist: https://gist.github.com/vaidik/051a197654fe4b0ecc80

Also read this article about relationships. I think you can achieve the same with Parent/Children docs but I haven't worked with them much.

Average and histogram aggregation on nested fields in elasticsearch

1 Answers