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from typing import Any, Callable, Type, TypeVar, Union, cast
from reactivex import Observable, compose
from reactivex import operators as ops
from reactivex.internal.utils import NotSet
from reactivex.typing import Accumulator
_T = TypeVar("_T")
_TState = TypeVar("_TState")
def reduce_(
accumulator: Accumulator[_TState, _T], seed: Union[_TState, Type[NotSet]] = NotSet
) -> Callable[[Observable[_T]], Observable[Any]]:
"""Applies an accumulator function over an observable sequence,
returning the result of the aggregation as a single element in the
result sequence. The specified seed value is used as the initial
accumulator value.
For aggregation behavior with incremental intermediate results, see
`scan()`.
Examples:
>>> res = reduce(lambda acc, x: acc + x)
>>> res = reduce(lambda acc, x: acc + x, 0)
Args:
accumulator: An accumulator function to be
invoked on each element.
seed: Optional initial accumulator value.
Returns:
An operator function that takes an observable source and returns
an observable sequence containing a single element with the
final accumulator value.
"""
if seed is not NotSet:
seed_: _TState = cast(_TState, seed)
scanner = ops.scan(accumulator, seed=seed_)
return compose(
scanner,
ops.last_or_default(default_value=seed_),
)
return compose(
ops.scan(cast(Accumulator[_T, _T], accumulator)),
ops.last(),
)
__all__ = ["reduce_"]
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