class_docstr: Defines count aggregation.
code: def __init__(self):
      super().__init__(
          init=lambda k: 0,
          accumulate_block=(
              lambda a, block: a
              + BlockAccessor.for_block(block).num_rows()
          ),
          merge=lambda a1, a2: a1 + a2,
          name="count()",
      )
  
imports: import math
  from typing import TYPE_CHECKING, Callable, List, Optional, Union
  from ray.data._internal.null_aggregate import _null_wrap_accumulate_block, _null_wrap_accumulate_row, _null_wrap_finalize, _null_wrap_init, _null_wrap_merge
  from ray.data._internal.sort import SortKey
  from ray.data.block import AggType, Block, BlockAccessor, KeyType, T, U
  from ray.util.annotations import PublicAPI
label_desc: Use image node_id 1 to create a new Count object from inherited base classes: AggregateFn with example: obj = Count()