title: How to convert pandas single column data frame to series or numpy vector
body: <p>I have the following data frame just single column.</p>
  
  <pre><code>import pandas as pd
  tdf =  pd.DataFrame({'s1' : [0,1,23.4,10,23]})
  </code></pre>
  
  <p>Currently it has the following shape.</p>
  
  <pre><code>In [54]: tdf.shape
  Out[54]: (5, 1)
  </code></pre>
  
  <p>How can I convert it to a Series or a numpy vector so that the shape is simply <code>(5,)</code></p>