title: Statistics: combinations in Python
body: <p>I need to compute combinatorials (nCr) in Python but cannot find the function to do that in <code>math</code>, <code>numpy</code> or <code>stat</code>  libraries. Something like a function of the type:</p>
  
  <pre><code>comb = calculate_combinations(n, r)
  </code></pre>
  
  <p>I need the number of possible combinations, not the actual combinations, so <code>itertools.combinations</code> does not interest me.</p>
  
  <p>Finally, I want to avoid using factorials, as the numbers I'll be calculating the combinations for can get too big and the factorials are going to be monstrous.</p>
  
  <p>This seems like a REALLY easy to answer question, however I am being drowned in questions about generating all the actual combinations, which is not what I want.</p>