title: in python pandas, how to unpack the lists in a column?
body: <p>i have a  python data frame, which contains 3 columns:</p>
  
  <pre><code>['date', 'country', 'dollar']
  </code></pre>
  
  <p>country is a string, which normally looks like 'singapore' 'ukraine' etc</p>
  
  <p>sometimes, country column's item is a list of countries, separated by |, such as </p>
  
  <pre><code>'US|UK|Germany'
  </code></pre>
  
  <p>the corresponding row will be:</p>
  
  <pre><code>20140101, 'US|UK|Germany', 123456
  </code></pre>
  
  <p>what i want is to 'unpack' the country column, and makes it strictly 1 country per row, the above row should be unpacked into 3 rows:</p>
  
  <pre><code>20140101, 'US', 123456
  20140101, 'UK', 123456
  20140101, 'Germany', 123456
  </code></pre>
  
  <p>is there any neat way to do this? </p>
  
  <p>thanks!</p>