Aggregation query syntax - assistance needed

[AClerk]

Hello
I am trying to get docs that answer the query.
But, also want to get 1 doc of each type.
For example, retrieve all the hostnames that have diskspace_usage > 0.3
With the following I am getting the correct results but with repetition.
I want to show each hostname once.
How should I write the query?

GET _search
{
"aggs" : {
    "hostnames" : {
            "terms" : { "field" : "hostname" ,
                        "size": 1
            } 
        }
    },
  "query": {
    "bool": {
      "must": [
            { "match": { "agent_type": "metricbeat" }},
            { "match": { "metricset_name": "filesystem" }},
			{"range": {"diskspace_usage": {
                                        "from": 0.3,
                                        "to": 1.0,
                                        "include_lower": true,
                                        "include_upper": false
                                    }
                                }
			},
                {
                    "range": {
                        "@timestamp": {
                            "from": "now-15m",
                            "to": null,
                            "include_lower": true,
                            "include_upper": true
                        }
                    }
                }
          ]
        }
    }
}

Cheers!