Slice numpy array into groups

Question

We have the following numpy array:

A = [[0,1,2,3],
[2,3,4,5],
[1,2,3,4],
[1,1,1,1],
[2,2,2,2],
[3,3,3,3],
[0,1,2,3],
[2,3,4,5],
[1,2,3,4],
 [10,10,10,10],
[20,20,20,20],
[30,30,30,30]]

I would like to create two new arrays:

B = [[0,1,2,3],
[2,3,4,5],
[1,2,3,4],
[0,1,2,3],
[2,3,4,5],
[1,2,3,4]]

and

C = [[1,1,1,1],
[2,2,2,2],
[3,3,3,3],
 [10,10,10,10],
[20,20,20,20],
[30,30,30,30]]

Basically I would like to split array A into two new arrays where B takes in groups of 3 rows, and array C takes the next groups of 3 rows.

create 2 functions f1 isIncreasingArray that takes an array and check if it's in increassing order by step 1. f2 isConstantArray checks if an array is constant. if both functions takes an array and return a bool you can use filter to get all the arrays that match that condition I could answer the question but I think that you might try solve it yourself — Ulises Bussi
– Ulises Bussi, Commented Nov 17, 2021 at 18:40
thank you for your comment, however it is not so clear to me: what exactly do you mean by checking if the array is constant? — relaxon
– relaxon, Commented Nov 17, 2021 at 18:47

sehan2 · Accepted Answer · 2021-11-17 18:47:34Z

2

There are probabily many different approaches to solve this, here is one:

import numpy as np
A = np.array([[0,1,2,3],
[2,3,4,5],
[1,2,3,4],
[1,1,1,1],
[2,2,2,2],
[3,3,3,3],
[0,1,2,3],
[2,3,4,5],
[1,2,3,4],
 [10,10,10,10],
[20,20,20,20],
[30,30,30,30]])

indices = np.reshape(np.arange(A.shape[0]),(-1,3))

B = A[indices[::2].flatten()]
C = A[indices[1::2].flatten()]

answered Nov 17, 2021 at 18:47

sehan2

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1 Comment

relaxon Over a year ago

thank you for your help!

Quang Hoang · Accepted Answer · 2021-11-17 18:48:42Z

2

Let's try:

tmp = A.reshape(-1, 3, A.shape[1])
B = tmp[::2]
C = tmp[1::2]

answered Nov 17, 2021 at 18:48

Quang Hoang

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2 Comments

relaxon Over a year ago

thank you for your help!

sehan2 Over a year ago

To get the output that is asked you have to do the following though: B.reshape(-1,4), C.reshape(-1,4)

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