add cumulative and/or incremental cardinality date histogram

[LeeDr]

Describe the feature: I've seen several requests in Elasticsearch and Kibana to query for cumulative or incremental cardinality counts over time and it doesn't currently seem possible. Several Elasticsearch developers discussed on Slack for over an hour and didn't really find a solution. Older discuss posts still show up in query results with no solutions.

For example;

date	user
2019-06-20	"a"
2019-06-20	"b"
2019-06-20	"c"
2019-06-21	"a"
2019-06-21	"d"

In the above docs, unique count on a daily date histogram buckets would show
2019-06-20 3
2019-06-21 2

But many people want to know new unique visitors to their website from their data. The cumulative values would be;
2019-06-20 3
2019-06-21 4 (because "a" was already counted on the 20th so "d" is new)

Or the incremental values would be;
2019-06-20 3
2019-06-21 1 (1 new unique visitor in this 2 day time span)

One example discuss post; https://discuss.elastic.co/t/how-can-i-get-a-date-histogram-cumulative-cardinality/58067

https://discuss.elastic.co/t/cardinality-over-date-histogram/171373

The next step would be to get Kibana to be able to use this type of aggregation for posts like this;
https://discuss.elastic.co/t/how-to-calculate-daily-new-users-to-a-website/186214

Most cases I've seen people just want the cardinality count. But they could actually want the unique values in some cases.

[elasticmachine]

Pinging @elastic/es-analytics-geo

[bargemb]

Looking forward for this feature

[jayaramcs]

@LeeDr Do you know if this is supported in Kibana at this time? I am unable to figure out how to do this and my search ultimately leads me here.

[LeeDr]

@jayaramcs So sorry but I missed that this was added (a year ago) and just now created a Kibana issue to add the functionality. elastic/kibana#70337
I'll follow up and try to move it along, but can't promise when it would make it in.
I'm really glad you pinged me on it!

Update: it sounds like this was already on the roadmap for Kibana team. I'll update again if I find another issue to track.

[jayaramcs]

Thank you @LeeDr .