ElasticSearch aggregation using array items as keys - elasticsearch

Question

Is it possible to create an aggregation by unnesting an array's elements to use as keys?
Here's an example:
Docs:
[
{
"languages": [ 1, 2 ],
"value": 100
},
{
"languages": [ 1 ],
"value": 50
}
]
its mapping:
{
"documents": {
"mappings": {
"properties": {
"languages": {
"type": "integer"
},
"value": {
"type": "integer"
}
}
}
}
}
and the expected output of a summing aggregation would be:
{
1: 150,
2: 100
}

Answer 1

You can achieve what you want by using a simple terms aggregation. Array elements will be bucketed individually:
POST index/_search
{
"aggs": {
"languages": {
"terms": {
"field": "languages"
},
"aggs": {
"total": {
"sum": {
"field": "value"
}
}
}
}
}
}
Results:
"aggregations" : {
"languages" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : 1,
"doc_count" : 2,
"total" : {
"value" : 150.0
}
},
{
"key" : 2,
"doc_count" : 1,
"total" : {
"value" : 100.0
}
}
]
}
}

Answer 2

The terms agg will sum up the # of occurences. What you want instead is a script to sum up the values based on the language array items as keys:
GET langs/_search
{
"size": 0,
"aggs": {
"lang_sums": {
"scripted_metric": {
"init_script": "state.lang_sums=[:]",
"map_script": """
for (def lang : doc['languages']) {
def lang_str = lang.toString();
def value = doc['value'].value;
if (state.lang_sums.containsKey(lang_str)) {
state.lang_sums[lang_str] += value;
} else {
state.lang_sums[lang_str] = value;
}
}
""",
"combine_script": "return state",
"reduce_script": "return states"
}
}
}
}
yielding
{
...
"aggregations":{
"lang_sums":{
"value":[
{
"lang_sums":{
"1":150,
"2":100
}
}
]
}
}
}