On Elasticsearch, how to aggregate based on the number of items in a field? - elasticsearch

Question

On Elasticsearch I have a field named Itinerary that can contain multiple values (from 1 up to 6), for example in the picture below there's 2 items in the field.
"Itinerary": [
{
"Carrier": "LH",
"Departure": "2021-07-04T06:55:00Z",
"Number": "1493",
"Arrival": "2021-07-04T08:40:00Z",
},
{
"Carrier": "LH",
"Departure": "2021-07-04T13:30:00Z",
"Number": "422",
"Arrival": "2021-07-04T16:05:00Z",
}
}
]
Is there a way I can aggregate based on the number of items in the field? Having something like:
1 item : 2
2 item : 4
...

Answer 1

Itinerary type needs to be define as nested type
"Itinerary":
{
"type": "nested"
}
Terms aggregation to group on a field. You can use script to get count of array or better introduce a field which has count of array
Top hits aggregation to get documents under that group
{
"size": 0,
"aggs": {
"NAME": {
"terms": {
"script": {
"source": "doc['Itinerary.Carrier.keyword'].length"
}
},
"aggs": {
"NAME": {
"top_hits": {
"size": 10
}
}
}
}
}
}
Result:
"aggregations" : {
"NAME" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : 2,
"doc_count" : 2,
"NAME" : {
"hits" : {
"total" : {
"value" : 2,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "index8",
"_type" : "_doc",
"_id" : "8OW1lnsBRh1xpgSkIOlq",
"_score" : 1.0,
"_source" : {
"Itinerary" : [
{
"Carrier" : "LH",
"Departure" : "2021-07-04T06:55:00Z",
"Number" : "1493",
"Arrival" : "2021-07-04T08:40:00Z"
},
{
"Carrier" : "LH",
"Departure" : "2021-07-04T13:30:00Z",
"Number" : "422",
"Arrival" : "2021-07-04T16:05:00Z"
}
]
}
},
{
"_index" : "index8",
"_type" : "_doc",
"_id" : "8uW6lnsBRh1xpgSkAun1",
"_score" : 1.0,
"_source" : {
"Itinerary" : [
{
"Carrier" : "LH2",
"Departure" : "2021-07-04T06:55:00Z",
"Number" : "14931",
"Arrival" : "2021-07-04T08:40:00Z"
},
{
"Carrier" : "LH2",
"Departure" : "2021-07-04T13:30:00Z",
"Number" : "4221",
"Arrival" : "2021-07-04T16:05:00Z"
}
]
}
}
]
}
}
},
{
"key" : 3,
"doc_count" : 1,
"NAME" : {
"hits" : {
"total" : {
"value" : 1,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "index8",
"_type" : "_doc",
"_id" : "8eW1lnsBRh1xpgSkdukQ",
"_score" : 1.0,
"_source" : {
"Itinerary" : [
{
"Carrier" : "LH1",
"Departure" : "2021-07-04T06:55:00Z",
"Number" : "14931",
"Arrival" : "2021-07-04T08:40:00Z"
},
{
"Carrier" : "LH1",
"Departure" : "2021-07-04T13:30:00Z",
"Number" : "4221",
"Arrival" : "2021-07-04T16:05:00Z"
},
{
"Carrier" : "LH1",
"Departure" : "2021-07-04T13:30:00Z",
"Number" : "3221",
"Arrival" : "2021-07-04T16:05:00Z"
}
]
}
}
]
}
}
}
]
}
}