title: Search the maximum value in a list of Series: ValueError: The truth value of a Series is ambiguous
body: <p>I need to find the maximum value among values in a list. Every element of this list is a pd.Series so when I use the function max(list) I get this error:</p>
  
  <blockquote>
    <p>"ValueError: The truth value of a Series is ambiguous. Use a.empty,
    a.bool(), a.item(), a.any() or a.all()."</p>
  </blockquote>
  
  <p>How can I avoid this problem?</p>
  
  <p>From a Dataframe that look like this:</p>
  
  <pre><code>             Date                Actual 
  0     2016-12-30 12:30:00          1800
  1     2016-12-30 13:00:00          1800
  2     2016-12-30 13:30:00          1600 
  .
  .
  .
  1256   201-05-30 13:30:00          1500
  </code></pre>
  
  <p>I create my list:</p>
  
  <pre><code>for single_date in datetime_range(start_date, end_date, timedelta(minutes=30)):
          b = find_nearest(df['Date'], single_date)
          row = df4[df4['Date'] == b ].index.tolist()  
          en=(df4.iloc[row]['Actual (kW)'])
          energy.append(en)
  </code></pre>
  
  <p>I need to find the maximum value in the list energy. Thank you</p>