Replace numbers in numpy array

Question

I have a numpy array populated with zeros and ones and after the array is created I need to replace some of the zeros with ones. Here is my code for the array:

grid = np.random.randint(0, 2, size=(4,4)) 
np.random.shuffle(grid)

I tried:

grid[grid == 0] = np.random.binomial(1, 0.9, size = None)

and:

grid[grid == 0] = np.random.randint(0, 2)

But then all the zeros are replaced with 1 or not replaced at all. Is there a way to replace only some of the zeros?

Yes, you need a way to identify just the elements/items that you want to replace - grid == 0 specifies all zeroes. There are a few ways that you can index an ndarray. - docs.scipy.org/doc/numpy/user/basics.indexing.html — wwii
– wwii, Commented Nov 30, 2017 at 16:37

paho · Accepted Answer · 2017-11-30 16:40:28Z

1

How about this:

grid += np.random.binomial(1, 0.9, size=grid.shape) * (grid == 0)

answered Nov 30, 2017 at 16:40

paho

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Uvar · Accepted Answer · 2017-11-30 16:38:18Z

1

Instead of a single draw, draw multiple times

grid = np.random.randint(0, 2, size=(4,4))
np.random.shuffle(grid)

grid[grid==0] = np.random.binomial(1, 0.5, size = grid[grid==0].shape[0])

answered Nov 30, 2017 at 16:38

Uvar

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Comments

manandearth · Accepted Answer · 2017-11-30 16:39:40Z

0

You better try again.

for me the shuffle method works.

np.random.shuffle(grid)

although seems to work only after applying it twice....

answered Nov 30, 2017 at 16:39

manandearth

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