Generate large number of random card decks - NumPy

Question

I need to generate a large number of random poker card decks. Speed is important so everything has to be in numpy matrix form.

I understand I can generate two cards

Answer 1

You can simulate np.random.choice(..., replace=False)'s behavior with a trick here based on argsort/argpartition. The idea is simple : We create a random array and sort it. The sorted indices thus obtained being unique would resemble np.random.choice(..., replace=False).

Since, we are looking to have a 2D array with such a feature, start with a random 2D array and for performance use np.argpartition for getting the first two sorted indices along each row to simulate 2 cards picking.

Thus, we would have a vectorized approach like so -

# N : Number of queries
# M : Number of cards to be picked
out = np.argpartition(np.random.rand(N,12*4),M,axis=1)[:,:M]

Runtime test -

In [55]: # Input params
    ...: N = 1000000 # Number of queries
    ...: M = 2 # Number of cards to be picked
    ...: 
    ...: def original_app(N,M):
    ...:     out = np.empty((N,2),dtype=int)
    ...:     for i in range(N):
    ...:         out[i] = np.random.choice(12*4,M, replace=False)
    ...:     return out
    ...: 
    ...: def vectorized_app(N,M):
    ...:     return np.argpartition(np.random.rand(N,12*4),M,axis=1)[:,:M]
    ...: 

In [56]: %timeit original_app(N,M)
1 loops, best of 3: 12.7 s per loop

In [57]: %timeit vectorized_app(N,M)
1 loops, best of 3: 678 ms per loop