ElasticSearch - Return unique result by field values - elasticsearch

Question

I have 3 "places" having each a type and a location:
PUT places
{
"mappings": {
"test": {
"properties": {
"type": { "type": "keyword" },
"location": { "type": "geo_point" }
}
}
}
}
POST places/test
{
"type" : "A",
"location": {
"lat": 1.378446,
"lon": 103.763427
}
}
POST places/test
{
"type" : "B",
"location": {
"lat": 1.478446,
"lon": 104.763427
}
}
POST places/test
{
"type" : "A",
"location": {
"lat": 1.278446,
"lon": 102.763427
}
}
I'd like to retrieve only one place per "type": the closest from a random position lets say "lat": 1.178446, "lon": 101.763427
In my example result answer should be composed by exactly 2 elements (one for "type: A" and one for "type: B").
I'd also prefer to avoid "aggregations" as I will need the _source of each places.
Any help would be great.

Answer 1

Without an aggregation, such an operation seems impossible executing one query.
This can be achieved with the top-hits-aggregation.
The following has been tested with elasticsearch 6:
POST /places/_search?size=0
{
"aggs" : {
"group-by-type" : {
"terms" : { "field" : "type" },
"aggs": {
"min-distance": {
"top_hits": {
"sort": {
"_script": {
"type": "number",
"script": {
"source": "def x = doc['location'].lat; def y = doc['location'].lon; return Math.abs(x-1.178446) + Math.abs(y-101.763427)",
"lang": "painless"
},
"order": "asc"
}
},
"_source": {
"includes": [ "type", "location" ]
},
"size" : 1
}
}
}
}
}
}
Note, I calculated the distance as: |location.x - givenPoint.x| + |location.y - givenPoint.y|
This is the response:
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 3,
"max_score": 0.0,
"hits": []
},
"aggregations": {
"group-by-type": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [{
"key": "A",
"doc_count": 2,
"min-distance": {
"hits": {
"total": 2,
"max_score": null,
"hits": [{
"_index": "places",
"_type": "test",
"_id": "3",
"_score": null,
"_source": {
"location": {
"lon": 102.763427,
"lat": 1.278446
},
"type": "A"
},
"sort": [1.1000006934661934]
}]
}
}
}, {
"key": "B",
"doc_count": 1,
"min-distance": {
"hits": {
"total": 1,
"max_score": null,
"hits": [{
"_index": "places",
"_type": "test",
"_id": "2",
"_score": null,
"_source": {
"location": {
"lon": 104.763427,
"lat": 1.478446
},
"type": "B"
},
"sort": [3.3000007411499093]
}]
}
}
}]
}
}
}