title: obtaining last value of dataframe column without index
body: <p>Suppose I have a DataFrame such as:</p>
  <pre><code>df = pd.DataFrame(np.random.randn(10,5), columns = ['a','b','c','d','e'])
  </code></pre>
  <p>and I would like to retrieve the last value in column <code>e</code>. I could do:</p>
  <pre><code>df['e'].tail(1)
  </code></pre>
  <p>but this would return a series which has index 9 with it. Ideally, I just want to obtain the value as a number that I can work with directly. I could also do:</p>
  <pre><code>np.array(df['e'].tail(1))
  </code></pre>
  <p>but this would then require me to access/call the 0'th element of it before I can really work with it. Is there a more direct/easy way to do this?</p>