Is there a math nCr function in python?

Is there a math nCr function in python?

The following program calculates nCr in an efficient manner (compared to calculating factorials etc.)

import operator as op
from functools import reduce

def ncr(n, r):
    r = min(r, n-r)
    numer = reduce(op.mul, range(n, n-r, -1), 1)
    denom = reduce(op.mul, range(1, r+1), 1)
    return numer // denom  # or / in Python 2

As of Python 3.8, binomial coefficients are available in the standard library as math.comb:

>>> from math import comb
>>> comb(10,3)
120

Do you want iteration? itertools.combinations. Common usage:

>>> import itertools
>>> itertools.combinations(abcd,2)
<itertools.combinations object at 0x01348F30>
>>> list(itertools.combinations(abcd,2))
[(a, b), (a, c), (a, d), (b, c), (b, d), (c, d)]
>>> [.join(x) for x in itertools.combinations(abcd,2)]
[ab, ac, ad, bc, bd, cd]

If you just need to compute the formula, use math.factorial:

import math

def nCr(n,r):
    f = math.factorial
    return f(n) / f(r) / f(n-r)

if __name__ == __main__:
    print nCr(4,2)

In Python 3, use the integer division // instead of / to avoid overflows:

return f(n) // f(r) // f(n-r)

Output

6

Is there a math nCr function in python?

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *