title: How to filter rows containing a string pattern from a Pandas dataframe
body: <p>Assume we have a data frame in Python Pandas that looks like this:</p>
  
  <pre><code>df = pd.DataFrame({'vals': [1, 2, 3, 4], 'ids': [u'aball', u'bball', u'cnut', u'fball']})
  </code></pre>
  
  <p>Or, in table form:</p>
  
  <pre class="lang-none prettyprint-override"><code>ids    vals
  aball   1
  bball   2
  cnut    3
  fball   4
  </code></pre>
  
  <p>How do I filter rows which contain the key word "ball?" For example, the output should be:</p>
  
  <pre class="lang-none prettyprint-override"><code>ids    vals
  aball   1
  bball   2
  fball   4
  </code></pre>