Elasticsearch aggregation on values in nested list (array) - elasticsearch

Question

I have stored some values in Elasticsearch nested data type (an array) but without using key/value pair. An example record would be:
{
"categories": [
"Category1",
"Category2"
],
"product_name": "productx"
}
Now I want to run aggregation query to find out unique list of categories available. But all the examples I've seen pointed to mapping that has key/value. Is there any way I can use above schema as is or do I need to change my schema to something like this to run aggregation query
{
"categories": [
{"name": "Category1"},
{"name": "Category2"}
],
"product_name": "productx"
}

Answer 1

Well regarding JSON structure, you need to take a step back and figure out if you'd want list or key-value pairs.
Looking at your example, I don't think you need key-value pairs but again its something you may want to clarify by understanding your domain if there'd be some more properties for categories.
Regarding aggregation, as far as I know, aggregations would work on any valid JSON structure.
For the data you've mentioned, you can make use of the below aggregation query. Also I'm assuming the fields are of type keyword.
Aggregation Query
POST <your_index_name>/_search
{
"size": 0,
"aggs": {
"myaggs": {
"terms": {
"size": 100,
"script": {
"inline": """
def myString = "";
def list = new ArrayList();
for(int i=0; i<doc['categories'].length; i++){
myString = doc['categories'][i] + ", " + doc['product'].value;
list.add(myString);
}
return list;
"""
}
}
}
}
}
Aggregation Response
{
"took": 1,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0,
"hits": []
},
"aggregations": {
"myaggs": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "category1, productx",
"doc_count": 1
},
{
"key": "category2, productx",
"doc_count": 1
}
]
}
}
}
Hope it helps!