Painless access a value in an ArrayList

Question

Trying to work out how to access an item in an ArrayList.

I have the values in _source:

  "session_id" : [
    "19a7ec8d",
    "19a7ec8d"
  ],

As they are all duplicates (due to a faulty Grok script), I want to get rid of the duplicates:

I cannot workout how to access the value.

String old = ctx._source.session_id[0];
ctx._source.remove(\"session_id\");
ctx._source.session_id = old;

I have also tried:

String old = ctx._source.session_id.get(0);

String old = ctx._source.session_id.get(0).value()

String old = ctx._source.session_id[0].value()

String old = ctx._source.session_id.get(0).toString()

Thanks

Answer 1

You can use _update_by_query

Data:

"hits" : [
      {
        "_index" : "index7",
        "_type" : "_doc",
        "_id" : "zQPYkXEB9JyZpSui0FLw",
        "_score" : 1.0,
        "_source" : {
          "session_id" : [
            "19a7ec8d",
            "19a7ec8d"
          ]
        }
      }
    ]

Query:

POST index7/_update_by_query
{
  "script":{
    "source":"if(ctx._source.session_id instanceof List && ctx._source.session_id.size()>0) { def firstValue=ctx._source.session_id[0];ctx._source.session_id=firstValue;}"
  },
  "query":{
    "match_all":{} 
  }
}

Result:

"hits" : [
      {
        "_index" : "index7",
        "_type" : "_doc",
        "_id" : "zQPYkXEB9JyZpSui0FLw",
        "_score" : 1.0,
        "_source" : {
          "session_id" : "19a7ec8d"
        }
      }
    ]