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Update documentation for approx_histogram_k, skew, and kurtosis #764

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Update documentation for approx_histogram_k, skew, and kurtosis #764

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30 changes: 16 additions & 14 deletions docs/source/authoring_features/GroupBy.md
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Expand Up @@ -46,8 +46,8 @@ Chronon will look for a `ts` column from the input source.
## Sketching Aggregations

Sketching algorithms are used to approximate the values of an exact aggregation when the aggregation itself is not
scalable. `unique_count` and `percentile` aggregations are examples where getting exact value requires storing all raw
values, and hence not-scalable. `approx_unique_count` and `approx_percentile` aggregations utilize a bounded amount of
scalable. `unique_count`, `percentile`, and `histogram` aggregations are examples where getting exact value requires storing all raw
values, and hence not-scalable. `approx_unique_count`, `approx_percentile`, and `approx_histogram_k` aggregations utilize a bounded amount of
memory to estimate the value of the exact aggregation. We allow users to tune this trade-off between memory and accuracy
as a parameter to the `Aggregation`. Chronon as a policy doesn't encourage use of un-scalable aggregations.
`unique_count` and `histogram` are supported but discouraged due to lack of `scalability`.
Expand Down Expand Up @@ -133,18 +133,20 @@ Limitations:

## Table of properties for aggregations

|aggregation | input type | nesting allowed? | output type | reversible | parameters | bounded memory |
|-----------------------|------------------|------------------|-------------------|------------|--------------------|----------------|
| count | all types | list, map | long | yes | | yes |
| min, max | primitive types | list, map | input | no | | yes |
| top_k, bottom_k | primitive types | list, map | list<input,> | no | k | yes |
| first, last | all types | NO | input | no | | yes |
| first_k, last_k | all types | NO | list<input,> | no | k | yes |
| average, variance | numeric types | list, map | double | yes | | yes |
| histogram | string | list, map | map<string, long> | yes | k=inf | no |
| approx_unique_count | primitive types | list, map | long | no | k=8 | yes |
| approx_percentile | primitive types | list, map | list<input,> | no | k=128, percentiles | yes |
| unique_count | primitive types | list, map | long | no | | no |
| aggregation | input type | nesting allowed? | output type | reversible | parameters | bounded memory |
|-----------------------------------|-----------------|------------------|-------------------|------------|--------------------|----------------|
| count | all types | list, map | long | yes | | yes |
| min, max | primitive types | list, map | input | no | | yes |
| top_k, bottom_k | primitive types | list, map | list<input,> | no | k | yes |
| first, last | all types | NO | input | no | | yes |
| first_k, last_k | all types | NO | list<input,> | no | k | yes |
| average | numeric types | list, map | double | yes | | yes |
| variance, skew, kurtosis | numeric types | list, map | double | no | | yes |
| histogram | string | list, map | map<string, long> | yes | k=inf | no |
| approx_histogram_k | primitive_types | list, map | map<string, long> | yes | k=inf | yes |
| approx_unique_count | primitive types | list, map | long | no | k=8 | yes |
| approx_percentile | primitive types | list, map | list<input,> | no | k=128, percentiles | yes |
| unique_count | primitive types | list, map | long | no | | no |


## Accuracy
Expand Down