title: Getting average of rows in dataframe greater than or equal to zero
body: <p>I would like to get the average value of a row in a dataframe where I only use values greater than or equal to zero.</p>
  
  <p>For example:
  if my dataframe looked like:</p>
  
  <pre><code>df = pd.DataFrame([[3,4,5], [4,5,6],[4,-10,6]])
      3   4   5
      4   5   6
      4   -10 6
  </code></pre>
  
  <p>currently if I get the average of the row I write :</p>
  
  <pre><code>df['mean'] = df.mean(axis = 1)
  </code></pre>
  
  <p>and get:</p>
  
  <pre><code>3   4   5   4
  4   5   6   5
  4   -10 6   0
  </code></pre>
  
  <p>I would like to get a dataframe that only used values greater than zero to computer the average.  I would like a dataframe that looked like:</p>
  
  <pre><code>3   4   5   4
  4   5   6   5
  4   -10 6   5
  </code></pre>
  
  <p>In the above example -10 is excluded in the average.  Is there a command that excludes the -10?</p>