Multi-Dimensional Arrays in Python

[Penguin Guy]

I've got a multidimensional array:


>>> rows = [
... [ 1 , 2 , 3 ]
... [ 4 , 5 , 6 ]
... [ 7 , 8 , 9 ]
... ]


And I want to make a link to it, but from a column point of view:


>>> columns = [
... [ 1 , 4 , 7 ]
... [ 2 , 5 , 8 ]
... [ 3 , 6 , 9 ]
... ]


So that if I change columns, it'll effect rows:

>>> columns[1][2] = 'Hello World!'
>>> print rows[2][1]
Hello World!


The closest thing I could find was this:


columns = map(list, zip(*rows))

[Zugzwang]

Such a "linking" between lists is, as far as I know, not a feature that Python supports. Rather, you would implement something like that in form of a class, which you probably have to write yourself. Some hints on that can be found here: http://docs.python.org/reference/datamodel.html#emulating-container-types

[avidday]

numpy arrays support what I think you are trying to do:



In [1]: import numpy as np

In [2]: a=np.array([[0,1,2],[3,4,5]])

In [3]: b=a[:,1]

In [4]: print b
------> print(b)
[1 4]

In [5]: a[:,1]+=2

In [6]: print b
------> print(b)
[3 6]

[raffaele181188]

Tabular data (http://pypi.python.org/pypi/tabular/0.0.8) may also help you :D

[The Cog]

Numpy matrix operations might also help:

>>> import numpy as np
>>> m=np.matrix([[1,2,3],[4,5,6],[7,8,9]])
>>> m
matrix([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
>>> m.transpose()
matrix([[1, 4, 7],
[2, 5, 8],
[3, 6, 9]])
>>>

[Penguin Guy]

As I understand, the best solution would be to create a class - however classes are way to complicated for me so I settled for a function:



def flip(list):
newList = []
a = 0
while a < len(list[0]):
b = 0
column = []
while b < len(list):
column.append(list[b][a])
b += 1
newList.append(column)
a += 1
return newList


Thanks to everyone for all the help.

[peevishone]

I've got a multidimensional array:


>>> rows = [
... [ 1 , 2 , 3 ]
... [ 4 , 5 , 6 ]
... [ 7 , 8 , 9 ]
... ]
And I want to make a link to it, but from a column point of view:


>>> columns = [
... [ 1 , 4 , 7 ]
... [ 2 , 5 , 8 ]
... [ 3 , 6 , 9 ]
... ]
So that if I change columns, it'll effect rows:

>>> columns[1][2] = 'Hello World!'
>>> print rows[2][1]
Hello World!The closest thing I could find was columns = zip(*rows), but that doesn't help me since it doesn't link the two. Anyone know how I can do this?

rows = [[ 1 , 2 , 3 ], [ 4 , 5 , 6 ], [ 7 , 8 , 9 ]]
columns = [[ rows[0][0] , rows[1][0] , rows[2][0] ], [rows[0][1] , rows[1][1] , rows[2][1] ], [rows[0][2] , rows[1][2] , rows[2][2] ]]

[jpkotta]

rows = [[ 1 , 2 , 3 ], [ 4 , 5 , 6 ], [ 7 , 8 , 9 ]]
columns = [[ rows[0][0] , rows[1][0] , rows[2][0] ], [rows[0][1] , rows[1][1] , rows[2][1] ], [rows[0][2] , rows[1][2] , rows[2][2] ]]

But that doesn't do what OP wanted. You need an extra layer of indirection. The simplest way is to make the elements of the matrix 1 element lists.



a = [[[1],[2]],[[3],[4]]]
b = [[a[0][0],a[1][0]],[a[0][1],a[1][1]]]
a[0][0][0] = 2



a: [[[2], [2]], [[3], [4]]]
b: [[[2], [3]], [[2], [4]]]

The correct way is to use something like numpy or roll your own class, as others have suggested.

[Penguin Guy]

I'm finished the project that I needed this for - the function I wrote worked just fine. But if someone could point me to a good example of a class similar to the one I'm looking for, I would be grateful - if only for educational purposes.