Split an array in rows and columns

Question

Using Python 2.

I need to split an array into their rows and columns but I don't seem to get the solution as asked in the exercise

import numpy as np
a = np.array([[5, 0, 3, 3],
 [7, 9, 3, 5],
 [2, 4, 7, 6],
 [8, 8, 1, 6]])

So far I have these functions

def _rows(a):
    print("array:"+ str(a[:,]))
_rows(a)
def _col(a):
    alt=a.T
    print ("array:"+ str(alt[:,]))
_col(a)

but I need to return a list and when I use the list() function it separe each individual character

I need the result to be:

[array([5, 0, 3, 3]), array([7, 9, 3, 5]), array([2, 4, 7, 6]), array([8, 8, 1, 6])]

[array([5, 7, 2, 8]), array([0, 9, 4, 8]), array([3, 3, 7, 1]), array([3, 5, 6, 6])]

yatu · Accepted Answer · 2019-07-02 13:08:02Z

8

You can unpack the rows and columns into a list with:

res1, res2 = [*a], [*a.T]

print(res1)

[array([5, 0, 3, 3]),
 array([7, 9, 3, 5]),
 array([2, 4, 7, 6]),
 array([8, 8, 1, 6])]

print(res2)

[array([5, 7, 2, 8]),
 array([0, 9, 4, 8]),
 array([3, 3, 7, 1]),
 array([3, 5, 6, 6])]

Extended iterable unpacking was introduced in python 3.0, for older versions you can call the list constructor as in @U9-Forward 's answer

edited Jul 2, 2019 at 13:08

answered Jul 2, 2019 at 12:53

yatu

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6 Comments

Gonzalo de Quesada Over a year ago

thanks, do I have to import something to be able to use the * because it gives me a syntax error

yatu Over a year ago

I'm guessing you have python 2. This was introduced in python 3. Let me add some alternative for older versions @GonzalodeQuesada

Gonzalo de Quesada Over a year ago

thanks, I also have python 3 but I'm trying to solve an error regarding the numpy import, so, for now, I'm using python 2

nicola Over a year ago

Just list(a) works. [*a] doesn't work for python 3.4.4 (nor for python 2). In older python3 the error is SyntaxError: can use starred expression only as assignment target.

yatu Over a year ago

doesn't work for python 3.4.4 sure it does. It was introduced in python 3.0 @nicola

|

U13-Forward · Accepted Answer · 2019-07-02 13:04:43Z

2

As it seems you're on Python 2:

>>> l1, l2 = list(a), list(a.T)
>>> l1
[array([5, 0, 3, 3]), array([7, 9, 3, 5]), array([2, 4, 7, 6]), array([8, 8, 1, 6])]
>>> l2
[array([5, 7, 2, 8]), array([0, 9, 4, 8]), array([3, 3, 7, 1]), array([3, 5, 6, 6])]
>>>

answered Jul 2, 2019 at 13:04

U13-Forward

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