title: Find length of longest string in Pandas dataframe column
body: <p>Is there a faster way to find the length of the longest string in a Pandas DataFrame than what's shown in the example below?</p>
  
  <pre><code>import numpy as np
  import pandas as pd
  
  x = ['ab', 'bcd', 'dfe', 'efghik']
  x = np.repeat(x, 1e7)
  df = pd.DataFrame(x, columns=['col1'])
  
  print df.col1.map(lambda x: len(x)).max()
  # result --&gt; 6
  </code></pre>
  
  <p>It takes about 10 seconds to run <code>df.col1.map(lambda x: len(x)).max()</code> when timing it with IPython's <code>%timeit</code>.</p>