How to transform a 3d arrays into a dataframe in python

Question

I have a 3d array as follows:

    ThreeD_Arrays = np.random.randint(0, 1000, (5, 4, 3))
    
    array([[[715, 226, 632],
            [305,  97, 534],
            [ 88, 592, 902],
            [172, 932, 263]],

           [[895, 837, 431],
            [649, 717,  39],
            [363, 121, 274],
            [334, 359, 816]],

           [[520, 692, 230],
            [452, 816, 887],
            [688, 509, 770],
            [290, 856, 584]],

           [[286, 358, 462],
            [831,  26, 332],
            [424, 178, 642],
            [955,  42, 938]], 

           [[ 44, 119, 757],
            [908, 937, 728],
            [809,  28, 442],
            [832, 220, 348]]])

Now I would like to have it into a DataFrame like this:

Add a Date column like indicated and the column names A, B, C.

How to do this transformation? Thanks!

Answer 1

Based on the answer to this question, we can use a MultiIndex. First, create the MultiIndex and a flattened DataFrame.

A = np.random.randint(0, 1000, (5, 4, 3))

names = ['x', 'y', 'z']
index = pd.MultiIndex.from_product([range(s)for s in A.shape], names=names)
df = pd.DataFrame({'A': A.flatten()}, index=index)['A']

Now we can reshape it however we like:

df = df.unstack(level='x').swaplevel().sort_index()
df.columns = ['A', 'B', 'C']
df.index.names = ['DATE', 'i']

This is the result:

          A    B    C
DATE i           
0    0  715  226  632
     1  895  837  431
     2  520  692  230
     3  286  358  462
     4   44  119  757
1    0  305   97  534
     1  649  717   39
     2  452  816  887
     3  831   26  332
     4  908  937  728
2    0   88  592  902
     1  363  121  274
     2  688  509  770
     3  424  178  642
     4  809   28  442
3    0  172  932  263
     1  334  359  816
     2  290  856  584
     3  955   42  938
     4  832  220  348