Insert in a list random of 0 and 1 with a certain number of 1's

Question

How do I generate a list of length N with random 0 and 1 values , but with a given number of 1\'s put randomly in the list.

For example, I want a list of 10

Answer 1

Using numpy

import numpy as np
from random import shuffle
A = np.ones(7, dtype=np.int)          // [1 1 1 1 1 1 1] and data-type as integer
B = np.zeros(3, dtype=np.int)         // [0 0 0] and data-type as integer
C = np.concatenate((A, B), axis = 0)  // [1 1 1 1 1 1 1 0 0 0]
shuffle(C)                            // [1 0 0 1 1 1 1 0 1 1]
print C

Answer 2

I like the shuffle() approach in the other answers; however, there is another way that uses fewer calls to the random number generator. Start with a list of zeros. Then use sample() to pick the 7 indicies that should be set to ones:

>>> from random import sample
>>> result = [0] * 10
>>> for i in sample(range(10), k=7):
        result[i] = 1

>>> result
[1, 0, 1, 1, 0, 1, 1, 1, 1, 0]

Answer 3

An approach not using random.shuffle:

import random
random.sample([0]*3 + [1]*7, 10) # [1, 1, 1, 1, 0, 0, 0, 1, 1, 1]

Answer 4

You can make the list have the right number of 0's and 1's pretty easily

data = [0] * 3 + [1] * 7

and then use random.shuffle to make their positions within the list random

from random import shuffle
shuffle(data)
print data

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