title: How to "cut off the tail" of a series
body: <p>I have a list of 10 terms with their scores. The first x tend to be much more important than the rest. So I want to find x.</p>
  
  <p>For example, <a href="http://www.chartgo.com/get.do?id=60ed576003" rel="nofollow">plotting this list</a> shows a plateau after third term. Hence we keep the first 3 terms. Even intuitively, keeping first 3 terms seems appropriate. </p>
  
  <pre><code>    badge                                   =&gt;    7.00709342956543
      unlocked                                =&gt;    7.00709342956543
      foursquare                              =&gt;   5.830315748850505
      https                                   =&gt;   5.001254081726074
      you've unlocked                         =&gt;   4.954763253529866
      50xxxxxx badge                          =&gt;   4.954763253529866
      all badges                              =&gt;   4.954763253529866
      unlocked far                            =&gt;   4.954763253529866
      badges                                  =&gt;   4.954763253529866
      just unlocked                           =&gt;   4.954763253529866
  </code></pre>
  
  <p>But how to generate this cutoff <strong>programmatically</strong>? I prefer stuff available in standard libraries.</p>