title: python pandas: split comma-separated column into new columns - one per value
body: <p>I have a dataframe like this:</p>
  
  <pre><code>data = np.array([["userA","event2, event3"],
              ['userB',"event3, event4"],
              ['userC',"event2"]])
  
  data = pd.DataFrame(data)
  
          0         1
  0   userA   "event2, event3"
  1   userB   "event3, event4"
  2   userC   "event2"
  </code></pre>
  
  <p>now I would like to get a dataframe like this:</p>
  
  <pre><code>       0    event2      event3      event4
  0   userA     1           1
  1   userB                 1           1
  2   userC     1
  </code></pre>
  
  <p>can anybody help please?</p>