python - Repeat NumPy array without replicating data?

Question

I'd like to create a 1D NumPy array that would consist of 1000 back-to-back repetitions of another 1D array, without replicating the data 1000 times.

Is it possible?

If it helps, I intend to treat both arrays as immutable.

Answer 1

You can't do this; a NumPy array must have a consistent stride along each dimension, while your strides would need to go one way most of the time but sometimes jump backwards.

The closest you can get is either a 1000-row 2D array where every row is a view of your first array, or a flatiter object, which behaves kind of like a 1D array. (flatiters support iteration and indexing, but you can't take views of them; all indexing makes a copy.)

Setup:

import numpy as np
a = np.arange(10)

2D view:

b = np.lib.stride_tricks.as_strided(a, (1000, a.size), (0, a.itemsize))

flatiter object:

c = b.flat