Statistics: combinations in Python

Question

I need to compute combinatorials (nCr) in Python but cannot find the function to do that in math, numpy or stat libraries. Something

Answer 1

That's probably as fast as you can do it in pure python for reasonably large inputs:

def choose(n, k):
    if k == n: return 1
    if k > n: return 0
    d, q = max(k, n-k), min(k, n-k)
    num =  1
    for n in xrange(d+1, n+1): num *= n
    denom = 1
    for d in xrange(1, q+1): denom *= d
    return num / denom