title: Export summary table of statsmodels regression results as csv
body: <p>Let's say I have three statsmodels <code>OLS</code> objects that I want to compare side by side. I can use <code>summary_col</code> to create a summary table that I can print out as text or export to latex.</p>
  <p>How can I export this table as csv?</p>
  <p>Here's a replicable example of what I want to do:</p>
  <pre class="lang-py prettyprint-override"><code># Libraries
  import pandas as pd
  import statsmodels.api as sm
  from statsmodels.iolib.summary2 import summary_col
  
  # Load silly data and add constant
  df = sm.datasets.stackloss.load_pandas().data
  df['CONSTANT'] = 1
  
  # Train three silly models
  m0 = sm.OLS(df['STACKLOSS'], df[['CONSTANT','AIRFLOW']]).fit()
  m1 = sm.OLS(df['STACKLOSS'], df[['CONSTANT','AIRFLOW','WATERTEMP']]).fit()
  m2 = sm.OLS(df['STACKLOSS'], df[['CONSTANT','AIRFLOW','WATERTEMP','ACIDCONC']]).fit()
  
  # Results table
  res = summary_col([m0,m1,m2], regressor_order=m2.params.index.tolist())
  print(res)
  
      ================================================
                STACKLOSS I STACKLOSS II STACKLOSS III
      ------------------------------------------------
      CONSTANT  -44.1320    -50.3588     -39.9197     
                (6.1059)    (5.1383)     (11.8960)    
      AIRFLOW   1.0203      0.6712       0.7156       
                (0.1000)    (0.1267)     (0.1349)     
      WATERTEMP             1.2954       1.2953       
                            (0.3675)     (0.3680)     
      ACIDCONC                           -0.1521      
                                         (0.1563)     
      ================================================
      Standard errors in parentheses.
  </code></pre>
  <p>Is there a way to export <code>res</code> to csv?</p>