title: Python: How to get the statistics of the position of each item in multiple lists?
body: <p>I want to analyze the sequences items of the items and the positions in the sequence where the item appear. </p>
  
  <p>For example:</p>
  
  <pre><code>dataframe['sequence_list'][0] = ['a','b', 'f', 'e']
  dataframe['sequence_list'][1] = ['a','c', 'd', 'e']
  dataframe['sequence_list'][2] = ['a','d']
  ...
  dataframe['sequence_list'][i] = ['a','b', 'c']
  </code></pre>
  
  <p>What I want to get is:
  How many times 'a' appear in position 0, 1, 2, 3 of the list ?
  How many times 'b' appear in position 0, 1, 2, 3 of the list ?
  ...</p>
  
  <p>Output would be like:</p>
  
  <pre><code>output[1,'a'] = 4
  output[2,'a'] = 0
  output[3,'a'] = 0
  output[4,'a'] = 0
  output[1,'b'] = 2
  ...  
  </code></pre>
  
  <p>The output format could be different. I just want to tell if there are any quick matrix computing methodology help me get the stats quickly?</p>