CODEWITHSUNDEEP
pythonrandom
strawberrycello
strawberrycello

Reputation: 47

random.choices() in python

I'd like to confirm that 

a = [random.choices([0,1],weights=[0.2,0.8],k=1) for i in range(0,10)]

does probabilistically the same thing as 

a = random.choices([0,1],weights=[0.2,0.8],k=10)

In particular, I expect both to make 10 independent draws from the set {0,1} with probability 0.2 on 0 and 0.8 on 1. Is this right?

Thanks!

Upvotes: 3

Views: 8718

Answers (2)

Dani Mesejo
Dani Mesejo

Reputation: 61930

As others have mentioned, the documentation is clear in regard to this aspect, you can further verified by setting the seed before each call, for example:

import random

random.seed(42)
print([random.choices([0, 1], weights=[0.2, 0.8], k=1)[0] for i in range(0, 10)])

random.seed(42)
print(random.choices([0, 1], weights=[0.2, 0.8], k=10))

Output

[1, 0, 1, 1, 1, 1, 1, 0, 1, 0]
[1, 0, 1, 1, 1, 1, 1, 0, 1, 0]

Furthermore setting just once, does leads to different results, as one might expect:

random.seed(42)
print([random.choices([0, 1], weights=[0.2, 0.8], k=1)[0] for i in range(0, 10)])
print(random.choices([0, 1], weights=[0.2, 0.8], k=10))

Output

[1, 0, 1, 1, 1, 1, 1, 0, 1, 0]
[1, 1, 0, 0, 1, 1, 1, 1, 1, 0]

Upvotes: 2

kingkupps
kingkupps

Reputation: 3534

The documentation seems to indicate the two are probabilistically the same and after running the following experiment:

from collections import defaultdict
import pprint
import random

results1 = defaultdict(int)
results2 = defaultdict(int)

for _ in range(10000):
    a = [random.choices([0,1],weights=[0.2,0.8],k=1) for i in range(0,10)]
    for sublist in a:
        for n in sublist:
            results1[n] += 1

for _ in range(10000):
    a = random.choices([0,1],weights=[0.2,0.8],k=10)
    for n in a:
        results2[n] += 1


print('first way 0s: {}'.format(results1[0]))
print('second way 0s: {}'.format(results2[0]))
print('first way 1s: {}'.format(results1[1]))
print('second way 1s: {}'.format(results2[1]))

I am seeing very similar results between the two methods.

Upvotes: 3

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