Get Percentage of Values in Elasticsearch - elasticsearch

Question

I have some test documents that look like
"hits": {
...
"_source": {
"student": "DTWjkg",
"name": "My Name",
"grade": "A"
...
"student": "ggddee",
"name": "My Name2",
"grade": "B"
...
"student": "ggddee",
"name": "My Name3",
"grade": "A"
And I wanted to get the percentage of students that have a grade of B, the result would be "33%", assuming there were only 3 students.
How would I do this in Elasticsearch?
So far I have this aggregation, which I feel like is close:
"aggs": {
"gradeBPercent": {
"terms": {
"field" : "grade",
"script" : "_value == 'B'"
}
}
}
This returns:
"aggregations": {
"gradeBPercent": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "false",
"doc_count": 2
},
{
"key": "true",
"doc_count": 1
}
]
}
}
I'm not looking necessarily looking for an exact answer, perhaps what I could terms and keywords I could google. I've read over the elasticsearch docs and not found anything that could help.

Answer 1

First off, you shouldn't need a script for this aggregation. If you want to limit your results to everyone where `value == 'B' then you should do that using a filter, not a script.
ElasticSearch won't return you a percentage exactly, but you can easily calculate that using the result from a TERMS AGGREGATION.
Example:
GET devdev/audittrail/_search
{
"size": 0,
"aggs": {
"a1": {
"terms": {
"field": "uIDRequestID"
}
}
}
}
That returns:
{
"took": 12,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 25083,
"max_score": 0,
"hits": []
},
"aggregations": {
"a1": {
"doc_count_error_upper_bound": 9,
"sum_other_doc_count": 1300,
"buckets": [
{
"key": 556,
"doc_count": 34
},
{
"key": 393,
"doc_count": 28
},
{
"key": 528,
"doc_count": 15
}
]
}
}
}
So what does that return mean?
the hits.total field is the total number of records matching your query.
the doc_count is telling you how many items are in each bucket.
So for my example here: I could say that the key "556" shows up in 34 of 25083 documents, so it has a percentage of (34 / 25083) * 100