create binary random matrix with probability in python

Question

I am new to python. I want to write a function which generates a random nxm binary matrix with each value 0 for probability p.

What I did.

def randbin(M,N,P):              # function to generate random binary matrix    
    mat = (np.random.rand(M,N)>=P).astype(int)
    return mat  

y = randbin(5,4,0.3)

Every time I print the output, I didn't get the result as per the estimated probability. I don't know what I am doing wrong.

Derlin · Accepted Answer · 2017-03-28 09:47:31Z

3

I don't see the problem with your method... A better way to generate a random matrix of 0s and 1s with a probability P of 0s is to use random.choice:

def randbin(M,N,P):  
    return np.random.choice([0, 1], size=(M,N), p=[P, 1-P])

To better understand, have a look at the random.choice documentation.

answered Mar 28, 2017 at 9:47

Derlin

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5 Comments

Derlin Over a year ago

If it works, please don't forget to mark the post as answered by ticking the checkmark on the left of my answer (and welcome to stack)

sumsan Over a year ago

Does the size is always a tuple. for example i wanted to create a binary matrix of size 100 in the above function. i.e. np.random.choice([0,1],size = (100). then it gave me an error: only length-1 arrays can be converted to Python scalar

Derlin Over a year ago

tuples are for matrices. For a 100x100 matrix, use size=(100, 100). For an array of 100 elements, use size=100 or size=(100,).

kmario23 Over a year ago

Sometimes this won't work. I get equal 0's & 1's sometimes though I give unequal probability.

Derlin Over a year ago

This is exactly what a probability will do ! When you flip a coin 10 times, you can have 10 faces, it happens. You need to read about probabilities if this behaviour troubles you.

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