title: Pandas: IndexingError: Unalignable boolean Series provided as indexer
body: <p>I'm trying to run what I think is simple code to eliminate any columns with all NaNs, but can't get this to work (<code>axis = 1</code> works just fine when eliminating rows):</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  
  df = pd.DataFrame({'a':[1,2,np.nan,np.nan], 'b':[4,np.nan,6,np.nan], 'c':[np.nan, 8,9,np.nan], 'd':[np.nan,np.nan,np.nan,np.nan]})
  
  df = df[df.notnull().any(axis = 0)]
  
  print df
  </code></pre>
  
  <p>Full error:</p>
  
  <p><code>raise IndexingError('Unalignable boolean Series provided as 'pandas.core.indexing.IndexingError: Unalignable boolean Series provided as indexer (index of the boolean Series and of the indexed object do not match</code></p>
  
  <p>Expected output:</p>
  
  <pre><code>     a    b    c
  0  1.0  4.0  NaN
  1  2.0  NaN  8.0
  2  NaN  6.0  9.0
  3  NaN  NaN  NaN
  </code></pre>