title: Pandas select all columns without NaN
body: <p>I have a DF with 200 columns. Most of them are with NaN's. I would like to select all columns with no NaN's or at least with the minimum NaN's. I've tried to drop all with a threshold or with notnull() but without success. Any ideas.</p>
  
  <pre><code>df.dropna(thresh=2, inplace=True)
  df_notnull = df[df.notnull()]
  </code></pre>
  
  <p>DF for example:</p>
  
  <pre><code>col1  col2 col3
  23     45  NaN
  54     39  NaN
  NaN    45  76
  87     32  NaN
  </code></pre>
  
  <p>The output should look like:</p>
  
  <pre><code> df.dropna(axis=1, thresh=2)
  
      col1  col2
      23     45  
      54     39  
      NaN    45  
      87     32  
  </code></pre>