title: Finding non-numeric rows in dataframe in pandas?
body: <p>I have a large dataframe in pandas that apart from the column used as index is supposed to have only numeric values:</p>
  
  <pre><code>df = pd.DataFrame({'a': [1, 2, 3, 'bad', 5],
                     'b': [0.1, 0.2, 0.3, 0.4, 0.5],
                     'item': ['a', 'b', 'c', 'd', 'e']})
  df = df.set_index('item')
  </code></pre>
  
  <p>How can I find the row of the dataframe <code>df</code> that has a non-numeric value in it? </p>
  
  <p>In this example it's the fourth row in the dataframe, which has the string <code>'bad'</code> in the <code>a</code> column. How can this row be found programmatically?</p>