title: Analyse python list with algorithm for counting occurences over date ranges
body: <p>The following shows the structure of some data I have (format: a list of lists)</p>
  
  <pre><code>data = 
  [ 
    [1,2008-12-01],
    [1,2008-12-01],
    [2,2008-12-01]
    ... (the lists continue)
  ]
  </code></pre>
  
  <p>The dates range from 2008-12-01 to 2008-12-25.</p>
  
  <p>The first field identifies a user by id, the second field (a date field) shows when this user visited a page on my site. </p>
  
  <p>I need to analyse this data so that i get the following results</p>
  
  <p>25 users visted on 1 day<br>
  100 users visted on 2 days<br>
  300 users visted on 4 days<br>
  ... upto 25 days</p>
  
  <p>I am using python and don't know where to start ! </p>
  
  <p><strong>EDIT</strong></p>
  
  <p>I'm sorry it seems I wasnt clear enough about what I needed as a few people have given answers that are not what I'm looking for. </p>
  
  <p>I need to find out how many users visited on all the days e.g.<br>
  10 users visited on 25 days (or every day)</p>
  
  <p>Then I'd like the to list the same for each frequency of days from 1 - 25. So as per my original example above<br>
  25 users visited for only one day (out of the 25)<br>
  100 users visited on 2 days (out of the 25)<br>
  etc </p>
  
  <p>I DONT need to know how many visited on each day<br>
  thanks</p>