Fill a numpy array with the same number? [duplicate]

Question

I know how to fill with zero in a 100-elements array:

np.zeros(100)

But what if I want to fill it with 9?

Answer 1

You can use:

a = np.empty(100)
a.fill(9)

or also if you prefer the slicing syntax:

a[...] = 9

np.empty is the same as np.ones, etc. but can be a bit faster since it doesn't initialize the data.

In newer numpy versions (1.8 or later), you also have:

np.full(100, 9)

Answer 2

If you just want same value throughout the array and you never want to change it, you could trick the stride by making it zero. By this way, you would just take memory for a single value. But you would get a virtual numpy array of any size and shape.

>>> import numpy as np
>>> from numpy.lib import stride_tricks
>>> arr = np.array([10])
>>> stride_tricks.as_strided(arr, (10, ), (0, ))
array([10, 10, 10, 10, 10, 10, 10, 10, 10, 10])

But, note that if you modify any one of the elements, all the values in the array would get modified.