title: Taking out a subpart from Enumerable
body: <p>I often want to take out a subpart from an Enumerable. The subpart is sometimes at the beginning and sometimes the end of the original Enumerable instance, and the length used to specify the subpart is sometimes that of the subpart and sometimes its complement. That gives four possibilities, but I only know how to do three of them. Is there a way to do the fourth one?</p>
  
  <p>1) Getting the first <code>n</code> elements:</p>
  
  <pre><code>[1, 2, 3, 4, 5].first(3) # =&gt; [1, 2, 3]    or
  [1, 2, 3, 4, 5].take(3) # =&gt; [1, 2, 3]
  </code></pre>
  
  <p>2) Dropping the first <code>n</code> elements:</p>
  
  <pre><code>[1, 2, 3, 4, 5].drop(3) #=&gt; [4, 5]
  </code></pre>
  
  <p>3) Getting the last <code>n</code> elements:</p>
  
  <pre><code>[1, 2, 3, 4, 5].last(3) #=&gt; [3, 4, 5]
  </code></pre>
  
  <p>4) Dropping the last <code>n</code> elements:</p>
  
  <pre><code>[1, 2, 3, 4, 5].some_method(3) #=&gt; [1, 2]
  </code></pre>