title: Decomposing trend, seasonal and residual time series elements
body: <p>I have a <code>DataFrame</code> with a few time series:</p>
  
  <pre><code>         divida    movav12       var  varmovav12
  Date                                            
  2004-01       0        NaN       NaN         NaN
  2004-02       0        NaN       NaN         NaN
  2004-03       0        NaN       NaN         NaN
  2004-04      34        NaN       inf         NaN
  2004-05      30        NaN -0.117647         NaN
  2004-06      44        NaN  0.466667         NaN
  2004-07      35        NaN -0.204545         NaN
  2004-08      31        NaN -0.114286         NaN
  2004-09      30        NaN -0.032258         NaN
  2004-10      24        NaN -0.200000         NaN
  2004-11      41        NaN  0.708333         NaN
  2004-12      29  24.833333 -0.292683         NaN
  2005-01      31  27.416667  0.068966    0.104027
  2005-02      28  29.750000 -0.096774    0.085106
  2005-03      27  32.000000 -0.035714    0.075630
  2005-04      30  31.666667  0.111111   -0.010417
  2005-05      31  31.750000  0.033333    0.002632
  2005-06      39  31.333333  0.258065   -0.013123
  2005-07      36  31.416667 -0.076923    0.002660
  </code></pre>
  
  <p>I want to decompose the first time series <code>divida</code> in a way that I can separate its trend from its seasonal and residual components.</p>
  
  <p>I found an answer <a href="https://stackoverflow.com/questions/20672236/time-series-decomposition-function-in-python">here</a>, and am trying to use the following code:</p>
  
  <pre><code>import statsmodels.api as sm
  
  s=sm.tsa.seasonal_decompose(divida.divida)
  </code></pre>
  
  <p>However I keep getting this error:</p>
  
  <pre><code>Traceback (most recent call last):
  File "/Users/Pred_UnBR_Mod2.py", line 78, in &lt;module&gt; s=sm.tsa.seasonal_decompose(divida.divida)
  File "/Library/Python/2.7/site-packages/statsmodels/tsa/seasonal.py", line 58, in seasonal_decompose _pandas_wrapper, pfreq = _maybe_get_pandas_wrapper_freq(x)
  File "/Library/Python/2.7/site-packages/statsmodels/tsa/filters/_utils.py", line 46, in _maybe_get_pandas_wrapper_freq
  freq = index.inferred_freq
  AttributeError: 'Index' object has no attribute 'inferred_freq'
  </code></pre>
  
  <p>How can I proceed?</p>