fix!: statistical functions should return null when provided a vector of only null values

[lbooker42]

Updated Numeric functions and tests:

• avg
• absAvg
• var
• wvar
• std
• wstd
• ste
• wste
• tstat
• wtstat
• median - had incorrect behavior when null values present
• percentile - had incorrect behavior when null values present
• cov
• cor

Updated UpdateBy aggregations and tests:

• RollingAvg
• RollingStd

Updated AggBy aggregations:

• avg
• var
• std
• ReVar
• ReAvg

Will close #5564

[rcaudy]

This is not ideal. The implementation of sort is sub-optimal:

1. We make one toArray() call internally.
2. Then we make an array of boxed values.
3. Then we sort using a comparator.
4. Then we make a third copy wherein we unbox the values.

Sorting on the vector at least let's us skip one of the copies.

We should write a separate ticket for updating the sort kernels in io.deephaven.engine.table.impl.sort to have a version that does not bother with a valuesToPermute chunk, and use that version for the implementation of sort. This way we make exactly one copyToArray() and we're done. Note copyToArray(), not toArray(): we mustn't sort our backing array.

[chipkent]

I gave this a look, and the stuff that jumped out at me is the stuff @rcaudy already commented on.

[chipkent]

Changes look good. We just need a resolution on the 2 array copies.

[rcaudy]

Minor comments, but approved regardless.

[deephaven-internal]

Labels indicate documentation is required. Issues for documentation have been opened:

Community: deephaven/deephaven-docs-community#239