field-collapsing.json

# Data
DELETE latest-connection
POST _bulk
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "10.10.10.10", "version": "1.3", "timestamp": "2018-05-01T12:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "20.20.20.20", "version": "1.5", "timestamp": "2018-05-01T12:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "10.10.10.10", "version": "1.4", "timestamp": "2018-05-02T12:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "10.10.10.10", "version": "1.4", "timestamp": "2018-05-03T12:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "30.30.30.30", "version": "1.0", "timestamp": "2018-05-03T10:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "30.30.30.30", "version": "1.3", "timestamp": "2018-05-03T12:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "20.20.20.20", "version": "1.5", "timestamp": "2018-05-04T12:10:30Z" }
{ "index" : { "_index" : "latest-connection", "_type" : "_doc"} }
{ "client": "20.20.20.20", "version": "1.6", "timestamp": "2018-05-04T12:11:30Z" }

# Simple
GET latest-connection/_search
{
    "query": {
        "match_all": { }
    },
    "collapse" : {
        "field" : "client.keyword"
    },
    "sort": [{"timestamp": "desc"}]
}

# Slightly more advanced
GET latest-connection/_search
{
    "query": {
        "match_all": { }
    },
    "collapse" : {
        "field" : "client.keyword",
        "inner_hits": {
          "name": "last_connection",
          "size": 1,
          "sort": [{"timestamp": "desc"}]
        }
    },
    "sort": [{"client.keyword": "asc"}, {"timestamp": "desc"}]
}