How to split a numpy array into arrays with specific number of elements

Question

I know that np.array_split allows us to split a NumPy array, but the number of elements in the split arrays only depends on the number of split chunks. The following example shows what I get and what I wish to get (the size of my_array is 35):

my_array = [1 1 1 1 1 0 0 0 1 1 0 1 1 1 0 1 0 1 0 0 0 0 1 0 0 1 0 1 1 0 0 1 1 1 1]
np.array_split(my_array, 5) outputs:

[array([1, 1, 1, 1, 1, 0, 0]),
 array([0, 1, 1, 0, 1, 1, 1]),
 array([0, 1, 0, 1, 0, 0, 0]),
 array([0, 1, 0, 0, 1, 0, 1]),
 array([1, 0, 0, 1, 1, 1, 1])]

AND 

np.array_split(my_array, 4) outputs:
[array([1, 1, 1, 1, 1, 0, 0, 0, 1]),
 array([1, 0, 1, 1, 1, 0, 1, 0, 1]),
 array([0, 0, 0, 0, 1, 0, 0, 1, 0]),
 array([1, 1, 0, 0, 1, 1, 1, 1])]

However, what I need is split arrays with 8 elements like this: 
[array([1, 1, 1, 1, 1, 0, 0, 0]),
 array([1, 1, 0, 1, 1, 1, 0, 1]),
 array([0, 1, 0, 0, 0, 0, 1, 0]),
 array([0, 1, 0, 1, 1, 0, 0, 1]),
 array([1, 1, 1])

I know that np.array_split(my_array, [8, 16, 24, 32]) can give me the answer for this specific question, but what I wish to do is that, for any size of an array, I could split it into arrays with a specific number of elements except for the last one if the array is not divisible.

Corralien · Accepted Answer · 2021-04-28 06:00:05Z

3

You are close:

my_array = np.arange(35)
N = 8

>>> np.array_split(my_array, range(N, len(my_array), N))
[array([0, 1, 2, 3, 4, 5, 6, 7]),
 array([ 8,  9, 10, 11, 12, 13, 14, 15]),
 array([16, 17, 18, 19, 20, 21, 22, 23]),
 array([24, 25, 26, 27, 28, 29, 30, 31]),
 array([32, 33, 34])]

answered Apr 28, 2021 at 6:00

Corralien

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Tim Roberts · Accepted Answer · 2021-04-28 05:51:43Z

0

np.array_split(my_array, (my_array.shape[0] + 7) // 8 )

You can of course generalize that to

np.array_split(my_array, (my_array.shape[0] + N - 1) // N )

answered Apr 28, 2021 at 5:51

Tim Roberts

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Carlos E Jimenez · Accepted Answer · 2021-04-28 06:33:45Z

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A possible solution would be to use the chunked function from more-itertools

list(chunked(my_array, N))

Returns a list of lists all with size N except, possibly, the last.

answered Apr 28, 2021 at 6:33

Carlos E Jimenez

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