Does the order of columns in the DataFrame matter?

[scidam]

Can't completely reproduce the problem. Below is working example:

import pandas as pd
import numpy as np
df = pd.DataFrame({'key1': ['Ohio', 'Ohio', 'Ohio', 'Nevada', 'Nevada'], 
                            'key2': [2000, 2001, 2002, 2001, 2002], 
                           'data': np.arange(5.)})  

gg = df.set_index(['key1', 'key2']).unstack('key1')

Output:
	data
key1	Nevada	Ohio
key2		
2000	NaN	0.0
2001	3.0	1.0
2002	4.0	2.0

gg.reindex([['data', 'data'],['Ohio', 'Nevada']], axis='columns')

Output:
	data
key1	Ohio	Nevada
key2		
2000	0.0	NaN
2001	1.0	3.0
2002	2.0	4.0

This works for pandas v. 1.0.1. Behavior can depend on Pandas version.