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What do you need self.values_agg for? It is only used for the aggregate of values not yet represented in cum_aggs if finalize is called. That value could just get computed right there on the fly.

Is it maybe for repeated finalize calls? To essentially re-use those computations?

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`values` might be quite large (up to W), without `values_agg` getting the current window value would be O(W) rather than O(1).

Note that there isn't a `finalize` call, only an `eval`, which gives the current aggregate over the window. You typically use these sliding window functions in a way where you want to get the current value every time the window moves.

yeah, I agree it's a bit distracting

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