Elasticsearch aggregation to retrieve array of values associated with another value - elasticsearch

Question

I am working with an Elasticsearch index with data like this:
"_source": {
"article_number": "123456",
"title": "Example item #1",
"attributes": [
{
"key": "Type",
"value": "Bag"
},
{
"key": "Color",
"value": "Grey"
}
]
},
"_source": {
"article_number": "654321",
"title": "Example item #2",
"attributes": [
{
"key": "Type",
"value": "Bag"
},
{
"key": "Color",
"value": "Red"
}
]
}
The goal is to dynamically generate search inputs in a page where there is one search input for each unique value of attributes.key and within that input one value for each corresponding value of attributes.value. So in this case I would want to render a "Type" input offering only the value "Bag" and a "Color" input offering the values "Grey" and "Red."
I am trying to accomplish this with an aggregation that will give me a unique set of all values of attributes.key along with an array of all the values of attributes.value that are associated with each key. An example of a result that would fit what I am hoping for would be this:
{
[
{
"key": "Type",
"values": [{
"name": "Bag",
"doc_count": 2
}]
},
{
"key": "Color",
"values": [{
"name": "Grey",
"doc_count": 1
},
{
"name": "Red",
"doc_count": 1
}]
}
}
I have tried nested and reverse nested aggregations, as well as composite aggregations, but so far without success.

Answer 1

Assuming your index mapping looks like this:
PUT attrs
{
"mappings": {
"properties": {
"attributes": {
"type": "nested",
"properties": {
"key": {
"type": "keyword"
},
"value": {
"type": "keyword"
}
}
}
}
}
}
you can achieve the desired results with the following combination of a nested terms aggregation and its sub-aggregation:
POST attrs/_search
{
"size": 0,
"aggs": {
"nested_context": {
"nested": {
"path": "attributes"
},
"aggs": {
"by_keys": {
"terms": {
"field": "attributes.key",
"size": 10
},
"aggs": {
"by_values": {
"terms": {
"field": "attributes.value",
"size": 10
}
}
}
}
}
}
}
}