code: def get_merge_idx_for_reducer_idx(self, reducer_idx: int) -> int:
      if (
          reducer_idx
          < (self.merge_partition_size + 1)
          * self._partitions_with_extra_task
      ):
          merge_idx = reducer_idx // (self.merge_partition_size + 1)
      else:
          reducer_idx -= (
              self.merge_partition_size + 1
          ) * self._partitions_with_extra_task
          merge_idx = (
              self._partitions_with_extra_task
              + reducer_idx // self.merge_partition_size
          )
      assert merge_idx < self.num_merge_tasks_per_round
      return merge_idx
  
imports: import logging
  import math
  from typing import Any, Callable, Dict, List, Optional, Tuple, TypeVar, Union
  import ray
  from ray.data._internal.block_list import BlockList
  from ray.data._internal.execution.interfaces import TaskContext
  from ray.data._internal.progress_bar import ProgressBar
  from ray.data._internal.remote_fn import cached_remote_fn
  from ray.data._internal.shuffle import ShuffleOp
  from ray.data.block import Block, BlockAccessor, BlockExecStats, BlockMetadata
  from ray.data.context import DataContext
  from ray.types import ObjectRef
  from ray.util.scheduling_strategies import NodeAffinitySchedulingStrategy
label_desc: Use image node_id 3 for calling the _MergeTaskSchedule obj's underlying member method code with example usage: obj.get_merge_idx_for_reducer_idx(reducer_idx) and returns: merge_idx