elasticsearch sort aggregation on categorical value - sorting

Question

In elasticsearch, I can aggregate and sort the aggregation on a second aggregation's numeric field.
e.g.
GET myindex/_search
{
"size":0,
"aggs": {
"a1": {
"terms": {
"field": "FIELD1",
"size":0,
"order": {"a2": "desc"}
},
"aggs":{
"a2":{
"sum":{
"field":"FIELD2"
}
}
}
}
}
}
However, I want to sort the aggregation on a categorical field value. ie. let's say the value of FIELD2 was one of ("a", "b", "c") -- I want to sort a1 first by all documents's with FIELD2: "a", then FIELD2: "b", then FIELD2: "c".
In my case, every FIELD1 has a unique FIELD2. So I really just want a way to sort the a1 results by FIELD2.

Answer 1

I am not sure what exactly you want but I tried following.
I created index with mapping
PUT your_index
{
"mappings": {
"your_type": {
"properties": {
"name": {
"type": "string"
},
"fruit" : {"type" : "string", "index": "not_analyzed"}
}
}
}
}
Then I indexed few documents like this
PUT your_index/your_type/1
{
"name" : "federer",
"fruit" : "orange"
}
Then I sorted all players with fruits with following aggregation
{
"size": 0,
"aggs": {
"a1": {
"terms": {
"field": "name",
"order": {
"_term": "asc"
}
},
"aggs": {
"a2": {
"terms": {
"field": "fruit",
"order": {
"_term": "asc"
}
}
}
}
}
}
}
The result I got is
"aggregations": {
"a1": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "federer",
"doc_count": 3,
"a2": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "green apple",
"doc_count": 1
},
{
"key": "orange",
"doc_count": 2
}
]
}
},
{
"key": "messi",
"doc_count": 2,
"a2": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "apple",
"doc_count": 1
},
{
"key": "banana",
"doc_count": 1
}
]
}
},
{
"key": "nadal",
"doc_count": 2,
"a2": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "blueberry",
"doc_count": 1
},
{
"key": "watermelon",
"doc_count": 1
}
]
}
},
{
"key": "ronaldo",
"doc_count": 2,
"a2": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "banana",
"doc_count": 1
},
{
"key": "watermelon",
"doc_count": 1
}
]
}
}
]
}
}
Make sure your FIELD2 is not_analyzed or you will get unexpected results.
Does this help?

Answer 2

I found a way that works. You must first aggregate on FIELD2, then on FIELD1.
{
"size": 0,
"aggs": {
"a2": {
"terms": {
"size": 0,
"field": "FIELD2",
"order": {
"_term": "asc"
}
},
"aggs": {
"a1": {
"terms": {
"size": 0,
"field": "FIELD1",
"order": {
"_term": "asc"
}
}
}
}
}
}
}