# \_source always zero in cardinality aggregation

**URL:** <https://discuss.elastic.co/t/source-always-zero-in-cardinality-aggregation/250677>\
**Category:** Elasticsearch\
**Created:** [October 1, 2020, 12:38pm UTC](https://discuss.elastic.co/t/source-always-zero-in-cardinality-aggregation/250677 "2020-10-01T12:38:01Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![autogenerated\_id](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/autogenerated_id/32/48390_2.png) [@autogenerated\_id](https://discuss.elastic.co/u/autogenerated_id)\
**Post date:** [October 2, 2020, 12:22pm UTC](https://discuss.elastic.co/t/source-always-zero-in-cardinality-aggregation/250677/5 "2020-10-02T12:22:24Z")

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Thanks for the help, it's much appreciated! I didn't know about `Debug.explain()`.

Let's dig into my use case step by step. Suppose an index has, among others, fields `left` and `right`. For starters, let's say we want to find out the number of distinct values in both `left` and `right` across all documents. That is, each value should be counted only once, even if it is found both in `left` and `right`. If we run two cardinality aggs and add the results together, some values may be counted twice. The only way I've found to do it (without returning all values and checking for duplicates by hand on the app side) is to run a scripted cardinality aggregation, where the script would be `[doc.left, doc.right]` (like [here](https://discuss.elastic.co/t/cardinality-aggregation-on-several-fields/34519)). This works fine.

However, the problem I'm dealing with is a bit more complex. I don't want to include all documents in the aggregation above, but `left` values based on one, and `right` values based on another criterion. So, take the index, apply `filter1` to it and pick only the `left` values of the resulting documents. Then apply `filter2` and pick only the `right` values of the documents that match. Finally, put all of these values in the same basket and find the number of distinct values.

Initially, I wanted to use named queries for this and just add an `if` to the script that would decide to return `doc.left`, `doc.right` or both, based on the matching queries. However, since this is [unsupported](https://discuss.elastic.co/t/terms-aggregation-on-named-queries/62595), I tried abusing document score to do the same thing (find out which filters matched based on the score). I failed because of the described behavior. Too bad, given that performance-wise it works fine.

I could also have two filter aggregations and compute cardinality on each of them, but then I wouldn't know how to combine the results with accounting for duplicates.

The only accurate way I can think of is returning to the application all distinct values of `left` with `filter1` applied, then doing the same for `right` and `filter2`, and finally computing the cardinality on the app side. This, however, would be too slow.

If you think there's a better way to solve this with reasonable performance, even by running multiple queries, I'd be interested to know.

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