title: index of non "NaN" values in Pandas
body: <p>From Pandas data frame, how to get index of non "NaN" values?</p>
  
  <p>My data frame is</p>
  
  <pre><code>    A    b     c
  0   1    q1    1
  1   2    NaN   3
  2   3    q2    3
  3   4    q1    NaN
  4   5    q2    7
  </code></pre>
  
  <p>And I want the index of the rows in which column <strong>b</strong> is not NaN. (there can be NaN values in other column e.g. c )</p>
  
  <blockquote>
    <p>non_nana_index = [0,2,3,4]</p>
  </blockquote>
  
  <p>Using this non "NaN" index list I want to create new data frame which column <strong>b</strong> do not have "Nan"</p>
  
  <p>df2=</p>
  
  <pre><code>    A    b     c
  0   1    q1    1
  1   3    q2    3
  2   4    q1    NaN
  3   5    q2    7
  </code></pre>