title: Error in groupby pandas
body: <p>I am running a script in windows and I get the following error:</p>
  
  <pre><code>  Traceback (most recent call last):    
    File "C:\Users\esalazar\Desktop\datos\stat_cea_2011\emas\amealco\promedios-emas.py", line 64, in &lt;module&gt;
      g=index.groupby(level=0)    
      AttributeError: 'NoneType' object has no attribute 'groupby'
  </code></pre>
  
  <p>I have installed pandas, scipy and numpy. I need to install some other library? How do I fix this error? </p>
  
  <p>This is part of my code:</p>
  
  <pre><code>data = pd.read_csv('C:/Users/esalazar/Desktop/datos/stat_cea_2011/emas/amealco/enero.csv',skiprows=1,names=['Fecha','Hora','C','D','E','Temperatura','TempRocio','DirViento','I','MagViento','K','Humedad','Presion','N','PreciAcu','P','Q','R','S'],header=0)
  Uviento=[]
  Vviento=[]
  
  for i in range(0,len(data['MagViento'])):
      Uviento.append((data['MagViento'][i]*sin((data['DirViento'][i]+180)*(pi/180.0))))
      Vviento.append((data['MagViento'][i]*cos((data['DirViento'][i]+180)*(pi/180.0))))
  
  data['PromeU']=Uviento
  data['PromeV']=Vviento
  
  data
  &lt;class 'pandas.core.frame.DataFrame'&gt; 
  Int64Index: 4463 entries, 0 to 4462
  Data columns (total 19 columns):
  Fecha          4463  non-null values
  Hora           4463  non-null values
  C              4463  non-null values
  D              4463  non-null values
  E              4463  non-null values
  Temperatura    4463  non-null values
  TempRocio      4463  non-null values
  DirViento      4463  non-null values
  I              4463  non-null values
  MagViento      4463  non-null values
  K              4463  non-null values
  Humedad        4463  non-null values
  Presion        4463  non-null values
  N              4463  non-null values
  PreciAcu       4463  non-null values
  P              4463  non-null values
  Q              4463  non-null values
  R              4463  non-null values
  S              4463  non-null values
  dtypes: float64(8), int64(4), object(7)
  
  df = data.set_index(['Fecha','Hora'],inplace=True)
  df
  </code></pre>
  
  <p>i get this error</p>
  
  <pre><code>TypeError: NoneType object has no atribute '--getitem--'
  </code></pre>
  
  <p>therefore,</p>
  
  <pre><code>grouped = df.groupby(level=0)
  </code></pre>
  
  <p>is error too.</p>