In the itertools module there is a recipe for returning a random combination from an iterable. Below are two versions of the code, one for Python 2.x and one for Python 3.x – in both cases you are using a generator which means that you are not creating a large iterable in memory.
Assumes Python 2.x
def random_combination(iterable, r):
"Random selection from itertools.combinations(iterable, r)"
pool = tuple(iterable)
n = len(pool)
indices = sorted(random.sample(xrange(n), r))
return tuple(pool[i] for i in indices)
In your case then it would be simple to do:
>>> import random
>>> def random_combination(iterable, r):
"Random selection from itertools.combinations(iterable, r)"
pool = tuple(iterable)
n = len(pool)
indices = sorted(random.sample(xrange(n), r))
return tuple(pool[i] for i in indices)
>>> n = 10
>>> m = 3
>>> print(random_combination(range(n), m))
(3, 5, 9) # Returns a random tuple with length 3 from the iterable range(10)
In the case of Python 3.x
In the case of Python 3.x you replace the xrange call with range but the use-case is still the same.
def random_combination(iterable, r):
"Random selection from itertools.combinations(iterable, r)"
pool = tuple(iterable)
n = len(pool)
indices = sorted(random.sample(range(n), r))
return tuple(pool[i] for i in indices)