text: Title: [BUG] df.loc[:, [fields]] triggered unnecessary iterative tiling
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  **Describe the bug**
  
  df.loc[:, [fields]] triggered unnecessary iterative tiling.
  
  **To Reproduce**
  To help us reproducing this bug, please provide information below:
  1. Your Python version
  2. The version of Mars you use
  3. Versions of crucial packages, such as numpy, scipy and pandas
  4. Full stack of the error.
  5. Minimized code to reproduce the error.
  
  ```python
  from mars.core import tile
  
  df2 = df[df['x'] < 1]
  loc_df = df2.loc[:, ['y', 'x']]
  tiled_loc_df = tile(loc_df)  # cannot run
  ```
  