title: Python TypeError: 'numpy.float64' object cannot be interpreted as an index
body: <p>Getting this error while using seasonal_decompose </p>
  
  <pre><code>from statsmodels.tsa.seasonal import seasonal_decompose
  decomposition = seasonal_decompose(ts_log)
  </code></pre>
  
  <p>this gives this error:</p>
  
  <pre><code>TypeError: 'numpy.float64' object cannot be interpreted as an index
  </code></pre>
  
  <p>ts_log is a time series </p>
  
  <pre><code>ts_log.index.dtype
  
  dtype('&lt;M8[ns]')
  </code></pre>
  
  <p>and </p>
  
  <pre><code>ts_log.head()
  Month
  1949-01-01    4.718499
  1949-02-01    4.770685
  1949-03-01    4.882802
  1949-04-01    4.859812
  1949-05-01    4.795791
  Name: #Passengers, dtype: float64
  
  ts_log.index
  DatetimeIndex(['1949-01-01', '1949-02-01', '1949-03-01', '1949-04-01',
             '1949-05-01', '1949-06-01', '1949-07-01', '1949-08-01',
             '1949-09-01', '1949-10-01',
             ...
             '1960-03-01', '1960-04-01', '1960-05-01', '1960-06-01',
             '1960-07-01', '1960-08-01', '1960-09-01', '1960-10-01',
             '1960-11-01', '1960-12-01'],
            dtype='datetime64[ns]', name=u'Month', length=144, freq=None)
  </code></pre>
  
  <p>converting #Passengers to int also gives the same error</p>