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from typing import Callable, List, Optional, TypeVar, cast
from reactivex import Observable, abc, typing
from reactivex.internal.basic import default_sub_comparer
_T = TypeVar("_T")
_TKey = TypeVar("_TKey")
def extrema_by(
source: Observable[_T],
key_mapper: typing.Mapper[_T, _TKey],
comparer: typing.SubComparer[_TKey],
) -> Observable[List[_T]]:
def subscribe(
observer: abc.ObserverBase[List[_T]],
scheduler: Optional[abc.SchedulerBase] = None,
) -> abc.DisposableBase:
has_value = False
last_key: _TKey = cast(_TKey, None)
items: List[_T] = []
def on_next(x: _T) -> None:
nonlocal has_value, last_key
try:
key = key_mapper(x)
except Exception as ex:
observer.on_error(ex)
return
comparison = 0
if not has_value:
has_value = True
last_key = key
else:
try:
comparison = comparer(key, last_key)
except Exception as ex1:
observer.on_error(ex1)
return
if comparison > 0:
last_key = key
items[:] = []
if comparison >= 0:
items.append(x)
def on_completed():
observer.on_next(items)
observer.on_completed()
return source.subscribe(
on_next, observer.on_error, on_completed, scheduler=scheduler
)
return Observable(subscribe)
def min_by_(
key_mapper: typing.Mapper[_T, _TKey],
comparer: Optional[typing.SubComparer[_TKey]] = None,
) -> Callable[[Observable[_T]], Observable[List[_T]]]:
"""The `min_by` operator.
Returns the elements in an observable sequence with the minimum key
value according to the specified comparer.
Examples:
>>> res = min_by(lambda x: x.value)
>>> res = min_by(lambda x: x.value, lambda x, y: x - y)
Args:
key_mapper: Key mapper function.
comparer: [Optional] Comparer used to compare key values.
Returns:
An observable sequence containing a list of zero or more
elements that have a minimum key value.
"""
cmp = comparer or default_sub_comparer
def min_by(source: Observable[_T]) -> Observable[List[_T]]:
return extrema_by(source, key_mapper, lambda x, y: -cmp(x, y))
return min_by
__all__ = ["min_by_"]
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