`loc` on MultiIndex row & column DataFrame returns wrong view of data

[pyrito]

System information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): macOS 12.2.1
• Modin version (modin.__version__): 0.15.2
• Python version: 3.9.12
• Code we can use to reproduce:

  
  import modin.pandas as pd
  import pandas

multi_index = pd.MultiIndex.from_tuples( [("r0", "rA"), ("r1", "rB")], names=["Courses", "Fee"] ) cols = pd.MultiIndex.from_tuples( [ ("Gasoline", "Toyota"), ("Gasoline", "Ford"), ("Electric", "Tesla"), ("Electric", "Nio"), ] ) data = [[100, 300, 900, 400], [200, 500, 300, 600]] df = pd.DataFrame(data, columns=cols, index=multi_index) pdf = pandas.DataFrame(data, columns=cols, index=multi_index)

pdf.loc[("r0"), ("Gasoline", "Toyota")] df.loc[("r0"), ("Gasoline", "Toyota")] # Returns wrong value

### Describe the problem
pandas returns this output:

Fee rA 100 Name: (Gasoline, Toyota), dtype: int64

whereas Modin gives us this:

100

The root of the issue seems to be in how we are handling `loc` lookups for MultiIndex DataFrames in the first place. The root of the issue seems to be different from the other MultiIndex issues we've had to deal with.

### Source code / logs
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[pyrito]

I did a bit of investigation here and it looks like ndim is 0 for this case, which appears to be the incorrect calculation. We may be having the incorrect abstraction for the MultiIndex case.

[eromoe]

I also come up same problem.

df2 = pd.DataFrame(np.arange(16).reshape(-1, 4), index=pd.MultiIndex.from_tuples(zip(list('zxzx'), [0,1,2,4]), names=['qq','ww']), columns=list('abcd'))
df3 = df2.unstack(0)

# modin
df3.loc[:, ['a']]
# pandas
df3._to_pandas().loc[:, ['a']]

# modin
df3.loc[:, [('a', 'x'), ('a', 'z')]]

# pandas
df3._to_pandas().loc[:, [('a', 'x'), ('a', 'z')]]

# modin
df3[['a']]

# pandas
df3._to_pandas()[['a']]