How to subtract aggregate min from aggreagate max(difference) in ES? - elasticsearch

Question

How to write an ES query to find the difference between max and min value of a field?
I am a newbee in elastic search,
In my case I feed lot of events along with session_id and time in to elastic search.
My event structure is
Event_name string `json:"Event_name"`
Client_id string `json:"Client_id"`
App_id string `json:"App_id"`
Session_id string `json:"Session_id"`
User_id string `json:"User_id"`
Ip_address string `json:"Ip_address"`
Latitude int64 `json:"Latitude"`
Longitude int64 `json:"Longitude"`
Event_time time.Time `json:"Time"`
I want to find the life time of a session_id based the feeded events.
For that I can retrive the maximum Event_time and minimum Event_time for a particular session_id by the following ES query.
{
"size": 0,
"query": {
"match": {
"Session_id": "dummySessionId"
}
},
"aggs": {
"max_time": {
"max": {
"field": "Time"
}
},
"min_time":{
"min": {
"field": "Time"
}
}
}
}
But what I exact want is (max_time - min_time)
How to write the ES query for the same????

Answer 1

Up to elasticsearch 1.1.1, this is not possible to do any arithmetic operation upon two aggregate function's reasult from elasticsearch side.
If you want then, you should do that from client side.
That is neither possible through scripts, as #eliasah suggests.
In the upcoming versions they may be add such facility.

Answer 2

in the 1.5.1 using the Scripted Metric Aggregation you can do this. Not sure about the performance, but it looks to work. This functionality is experimental and may be changed or removed completely in a future release.
POST test_time
POST test_time/data/1
{"Session_id":1234,"Event_time":"2014-01-01T12:00:00"}
POST test_time/data/3
{"Session_id":1234,"Event_time":"2014-01-01T14:00:00"}
GET /test_time/_search
{
"size": 0,
"aggs": {
"by_user": {
"terms": {
"field": "Session_id"
},
"aggs": {
"session_lenght_sec": {
"scripted_metric": {
"map_script": "_agg['v'] = doc['Event_time'].value",
"reduce_script": "min = null; max = null; for (a in _aggs) {if (min == null || a.v < min) { min = a.v}; if (max == null || a.v > max) { max = a.v }}; return (max-min)/1000"
}
}
}
}
}
}
###### RESPONSE #######
{
...,
"aggregations": {
"by_user": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": 1234,
"doc_count": 2,
"session_lenght_sec": {
"value": "7200"
}
}
]
}
}
}

Answer 3

This answer is bound to the Elasticsearch 7.8 version.
Followed up the #pippobaudos answer ahead. Elasticsearch has made some major changes since the answer.
the aggregation has a type 'scripted_metric' (click on the link to know more), which has new sub-attributes such as init_script, map_script, combine_script, reduce_script. Out of which, only init_script is optional. Following is the modified query.
"aggs": {
"cumulative":{
"scripted_metric": {
"init_script": {
"source": "state.stars = []"
},
"map_script": {
"source": "if (doc.containsKey('star_count')) { state.stars.add(doc['star_count'].value); }"
},
"combine_script": {
"source": "long min=9223372036854775807L,max=-9223372036854775808L; for (a in state.stars) {if ( a < min) { min = a;} if ( a > max) { max = a; }} return (max-min)"
},
"reduce_script": {
"source": "long max = -9223372036854775808L; for (a in states) { if (a != null && a > max){ max=a; } } return max "
}
}
}
}

Answer 4

Giving directly the query will not help you much, so I suggest you read the documentation about Script Fields and Scripting.