title: List of lists value in dictionary?
body: <p>Input file 'test.txt':</p>
  
  <pre><code>a 2012 fff
  
  b 2011 ttt
  
  a 2011 fff
  
  b 2012 sss
  
  a 2011 vvv
  </code></pre>
  
  <p>I have determined the following code to populate dictionary and sort values:</p>
  
  <pre><code>from collections import defaultdict
  res = defaultdict(list)
  with open('test.txt','r') as file:
      for line in file:
          field0, field1, field2 = line.split()
          res[field0] += [field1, field2]
  
  for i in res.keys():
      print i, sorted(res[i], key=lambda x: x[0])
  </code></pre>
  
  <p>However, this yields "a [2011, 2011, 2012, fff, fff, vvv]" and I want output to be in the exact same format as the input (but sorted):</p>
  
  <pre><code>a 2011 fff
  
  a 2011 vvv
  
  a 2012 fff
  </code></pre>
  
  <p>I can't just use sort on the original input since I will be referencing multiple times and need to store in memory. Should value for each line be stored in a list (ie. dictionary value is list of lists)?</p>