code: def reduce(objs: List[List]):
      """
      Spawn a concat task for 2d-list objects
  
      Parameters
      ----------
      objs: List
          2d-list of the partitioned dask task execution results, which will be concat.
  
      Returns
      -------
      obj:
          The spawning concat task.
      """
      return spawn(
          concat,
          args=([spawn(concat, args=(objs_d,)) for objs_d in objs],),
      )
  
file_path: mars/mars/contrib/dask/utils.py
imports: from typing import List
  from dask import is_dask_collection
  from dask.array.core import _concatenate2
  from dask.dataframe import concat
  from dask.utils import is_arraylike, is_dataframe_like, is_series_like, is_index_like
  from ...remote import spawn
label_desc: Use image node_id 2 for calling a global function with example usage: reduce(objs) and returns: spawn