title: Pandas fillna row wise?
body: <p>It'a simple example.</p>
  
  <pre><code>d=pd.DataFrame({'x':[1,None,None,3,4],'y':[3,2,3,None,7],'z':[None,None,None,None,None]})
  d['t']=d.mean(axis=1)
  
  Out[96]: 
       x    y     z    t
  0  1.0  3.0  None  2.0
  1  NaN  2.0  None  2.0
  2  NaN  3.0  None  3.0
  3  3.0  NaN  None  3.0
  4  4.0  7.0  None  5.5
  </code></pre>
  
  <p>I want to fill NA with the mean of the row.The mean of every row I have added<br>
  as <code>t</code>.The result I want is:</p>
  
  <pre><code>x y z 
  1 3 2
  2 2 2
  3 3 3
  3 3 3
  4 7 5.5
  </code></pre>