Python numpy reshape 3d list into 2d array

Question

I wish to convert

edit : the code below is a 3D list of list,

[
    [ 
        [
            [1,2,3,],
            [4,5,6,],
        ],
        [
            [7,8,9,],
            [10,11,12,], 
        ],
    ],
    [ 
        [
            [A,B,C,],
            [D,E,F,], 
        ],
        [
            [G,H,I,],
            [J,K,L,], 
        ],
    ],
]

Into

[

[1,2,3],
[4,5,6],
[7,8,9],
[10,11,12],
[A,B,C],
[D,E,F],
[G,H,I],
[J,K,L]

]

I have tried numpy.flatten but with no success https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.flatten.html

Since you have characters and numbers in your list, I recommend using pandas instead of numpy — anishtain4
– anishtain4, Commented Apr 23, 2019 at 14:25
What dtype do you want? What are A, B etc. As shown those are variables, not strings. As such they must have values, which in Python could be anything. Variable ids won't display in the actual list (or array). — hpaulj
– hpaulj, Commented Apr 23, 2019 at 16:31

Jurgen Strydom · Accepted Answer · 2019-04-23 12:12:07Z

2

Reshape is your tool.

Here is a self contained example:

import numpy as np
a = np.array([
    [[[1,2,3] , [4,5,6]],
     [[7,8,9] , [10,11,12]]],
    [[[13,14,15] , [16,17,18]],
     [[19,20,21] , [22,23,24]]]
    ])

a.shape
>>> (2, 2, 2, 3)

a.reshape(8,3)
>>> array([[ 1,  2,  3],
>>>        [ 4,  5,  6],
>>>        [ 7,  8,  9],
>>>        [10, 11, 12],
>>>        [13, 14, 15],
>>>        [16, 17, 18],
>>>        [19, 20, 21],
>>>        [22, 23, 24]])

answered Apr 23, 2019 at 12:12

Jurgen Strydom

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4 Comments

Dan Over a year ago

or a.reshape(-1,3) if you don't want to pre-calculate the number of rows.

Brigitte Maillère Over a year ago

Thanks Jurgen and @Dan . but I found that my code is a 3D list of lists, not a 3D array. I edited my question : how to convert 3D lit of list into a 2D array.

Dan Over a year ago

@BrigitteCharpent you can use np.array() and list to convert between the two and still use this method

Brigitte Maillère Over a year ago

Thanks to all of you. I had difficulties transforming eachlist level into an array level. Finally I simply iterated over my lists in plain simple Python.

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