max - 1 year ago 122
Python Question

NumPy array initialization (fill with identical values)

I need to create a NumPy array of length

`n`
, each element of which is
`v`
.

Is there anything better than:

``````a = empty(n)
for i in range(n):
a[i] = v
``````

I know
`zeros`
and
`ones`
would work for v = 0, 1. I could use
`v * ones(n)`
, but it won't work when
`v`
is
`None`
, and also would be much slower.

NumPy 1.8 introduced `np.full()`, which is a more direct method than `empty()` followed by `fill()` for creating an array filled with a certain value:

``````>>> np.full((3, 5), 7)
array([[ 7.,  7.,  7.,  7.,  7.],
[ 7.,  7.,  7.,  7.,  7.],
[ 7.,  7.,  7.,  7.,  7.]])

>>> np.full((3, 5), 7, dtype=int)
array([[7, 7, 7, 7, 7],
[7, 7, 7, 7, 7],
[7, 7, 7, 7, 7]])
``````

This is arguably the way of creating an array filled with certain values, because it explicitly describes what is being achieved (and it can in principle be very efficient since it performs a very specific task).

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