class ray.data.aggregate.Std(on: Optional[str] = None, ddof: int = 1, ignore_nulls: bool = True, alias_name: Optional[str] = None)[source]#

Bases: ray.data.aggregate._aggregate._AggregateOnKeyBase

Defines standard deviation aggregation.

Uses Welford’s online method for an accumulator-style computation of the standard deviation. This method was chosen due to its numerical stability, and it being computable in a single pass. This may give different (but more accurate) results than NumPy, Pandas, and sklearn, which use a less numerically stable two-pass algorithm. See https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Welford’s_online_algorithm

PublicAPI: This API is stable across Ray releases.