How to get min/max and avg lengths of text field?

Question

I have an index with the following mapping:

        "properties": {
            "content": {
                "type":  "text",                
            },
            "ar_name": {
                "type": "text"
            }

        }

I want to get statistics (min length, max length and average length) to the content field.

How can I do it ?

Answer 1

The string_stats aggregation provides that support but only for keyword fields. Since your content field is of type text, I assume it contains free-text that is not really suitable as keyword.

If that's the case, I would suggest that you stored the length of the content field in another integer field (e.g. content_length) that you can then use in a stats aggregation that would return you the metrics you expect.

Answer 2

If you want to keep field as text or you don't want to change the mapping, you can achieve this by a script in aggregation. Here is an example query:

{
  "size": 0,
  "aggs": {
    "min": {
      "min": {
        "script": {
          "source": """
            return doc['content'].value.length();
          """
        }
      }
    },
    "max": {
      "max": {
        "script": {
          "source": """
            return doc['content'].value.length();
          """
        }
      }
    },
    "avg": {
      "avg": {
        "script": {
          "source": """
            return doc['content'].value.length();
          """
        }
      }
    }
  }
}