Script to return array for scripted metric aggregation from combine - elasticsearch

Question

For scripted metric aggregation , in the example shown in the documentation , the combine script returns a single number.
Instead here , can i pass an array or hash ?
I tried doing it , though it did not return any error , i am not able to access those values from reduce script.
In reduce script per shard i am getting an instance when converted to string read as 'Script2$_run_closure1#52ef3bd9'
Kindly let me know , if this can be accomplished in any way.

Answer 1

At least for Elasticsearch version 1.5.1 you can do so.
For example, we can modify Elasticsearch example (scripted metric aggregation) to receive an average profit (profit divided by number of transactions):
{
"query": {
"match_all": {}
},
"aggs": {
"avg_profit": {
"scripted_metric": {
"init_script": "_agg['transactions'] = []",
"map_script": "if (doc['type'].value == \"sale\") { _agg.transactions.add(doc['amount'].value) } else { _agg.transactions.add(-1 * doc['amount'].value) }",
"combine_script": "profit = 0; num_of_transactions = 0; for (t in _agg.transactions) { profit += t; num_of_transactions += 1 }; return [profit, num_of_transactions]",
"reduce_script": "profit = 0; num_of_transactions = 0; for (a in _aggs) { profit += a[0] as int; num_of_transactions += a[1] as int }; return profit / num_of_transactions as float"
}
}
}
}
NOTE: this is just a demo for an array in the combine script, you can calculate average easily without using any arrays.
The response will look like:
"aggregations" : {
"avg_profit" : {
"value" : 42.5
}
}