This adds a new pipeline aggregation for calculating Kolmogorov–Smirnov test for a given sample and buckets path.
For now, the buckets path resolution needs to be `_count`. But, this may be relaxed in the future.
It accepts a parameter `fractions` that indicates the distribution of documents from some other pre-calculated sample.
This particular version of the K-S test is Two-sample, meaning, it calculates if the `fractions` and the distribution of `_count` values in the buckets_path are taken from the same distribution.
This in combination with the hypothesis alternatives (`less`, `greater`, `two_sided`) and sampling logic (`upper_tail`, `lower_tail`, `uniform`) allow for flexibility and usefulness when comparing two samples and determining the likelihood of them being from the same overall distribution.
Usage:
```
POST correlate_latency/_search?size=0&filter_path=aggregations
{
"aggs": {
"buckets": {
"terms": { <1>
"field": "version",
"size": 2
},
"aggs": {
"latency_ranges": {
"range": { <2>
"field": "latency",
"ranges": [
{ "to": 0.0 },
{ "from": 0, "to": 105 },
{ "from": 105, "to": 225 },
{ "from": 225, "to": 445 },
{ "from": 445, "to": 665 },
{ "from": 665, "to": 885 },
{ "from": 885, "to": 1115 },
{ "from": 1115, "to": 1335 },
{ "from": 1335, "to": 1555 },
{ "from": 1555, "to": 1775 },
{ "from": 1775 }
]
}
},
"ks_test": { <3>
"bucket_count_ks_test": {
"buckets_path": "latency_ranges>_count",
"alternative": ["less", "greater", "two_sided"]
}
}
}
}
}
}
```
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
