Accessors to retrieve first and last data points from TimeWeightSummary

[jerryxwu]

Creating this issue for tracebility.

A user on Stackoverflow asked to extract the first and the last point value and timestamp from a time_weight object. We think it make sense to add the same accessors to counter_agg as well. There's very little risk of exposing the internal structure of the objects as the first and the last data points are needed for the rollup functions.

Specifically, the following accessors are discussed:

• first_val / last_val
• first_time / last_time (perhaps consider naming them as first_at / last_at to be consistent with open_at, close_at, etc.

[rtwalker]

first_time / last_time (perhaps consider naming them as first_at / last_at to be consistent with open_at, close_at, etc.

This is a good point. Should we likewise consider (first|last) instead of (first|last)_val? Or are they too semantically different from the already existing first and last hyperfunctions?

[jerryxwu]

Should we likewise consider (first|last) instead of (first|last)_val? Or are they too semantically different from the already existing first and last hyperfunctions?

Good point. I think it makes sense.

[rtwalker]

Consensus from standup today:

• use first_val/last_val and first_time / last_time names
• change open_at and friends to open_time