得到输入PCollection中最大的元素 Args: pcollection (PCollection): 输入PCollection key (function, optional): 用于提取key的函数，与Python内置``max()``中的 ``key`` 参数相同 **options: 可配置选项 Returns: PObject: 包含最大元素的PObject >>> from bigflow import transforms >>> _p = _pipeline.para
(pcollection, key=None, **options)