How To De-interleave Array In Numpy?

I have a numpy array that is interleaved in a tricky way and I can't figure out an easy way to de-interleave it. Suppose the (84, 132) matrix is: 0 100 200 ... 1 101 201 ...

Solution 1:

Permute axes and reshape with the idea being borrowed off General idea for nd to nd transformation. -

N = 4 # number of rows to split with
n = a.shape[1]
a.reshape(-1,N,n).swapaxes(1,2).reshape(-1,n*N)

Solution 2:

You could do something like:

#!/usr/bin/env python                                                                               

import numpy as np

# construct test data                                                                               
i = np.arange(132)
j = np.arange(84)
ii, jj = np.meshgrid(i, j)
a = 100 * ii + jj

# the operation                                                                                     
n0, n1 = a.shape
m = 4
b = np.concatenate([a[:,i].reshape((n0 // m, m)) for i in range(n1)], axis=1)

gives:

>>> a
array([[    0,   100,   200, ..., 12900, 13000, 13100],
       [    1,   101,   201, ..., 12901, 13001, 13101],
       [    2,   102,   202, ..., 12902, 13002, 13102],
       ...,
       [   81,   181,   281, ..., 12981, 13081, 13181],
       [   82,   182,   282, ..., 12982, 13082, 13182],
       [   83,   183,   283, ..., 12983, 13083, 13183]])

>>> b
array([[    0,     1,     2, ..., 13101, 13102, 13103],
       [    4,     5,     6, ..., 13105, 13106, 13107],
       [    8,     9,    10, ..., 13109, 13110, 13111],
       ...,
       [   72,    73,    74, ..., 13173, 13174, 13175],
       [   76,    77,    78, ..., 13177, 13178, 13179],
       [   80,    81,    82, ..., 13181, 13182, 13183]])

A bit hard to see what is going on where elements are omitted above, so here is another case with a smaller array (8x12) where all elements can be shown

array([[  0, 100, 200, 300, 400, 500, 600, 700],
       [  1, 101, 201, 301, 401, 501, 601, 701],
       [  2, 102, 202, 302, 402, 502, 602, 702],
       [  3, 103, 203, 303, 403, 503, 603, 703],
       [  4, 104, 204, 304, 404, 504, 604, 704],
       [  5, 105, 205, 305, 405, 505, 605, 705],
       [  6, 106, 206, 306, 406, 506, 606, 706],
       [  7, 107, 207, 307, 407, 507, 607, 707],
       [  8, 108, 208, 308, 408, 508, 608, 708],
       [  9, 109, 209, 309, 409, 509, 609, 709],
       [ 10, 110, 210, 310, 410, 510, 610, 710],
       [ 11, 111, 211, 311, 411, 511, 611, 711]])

array([[  0,   1,   2,   3, 100, 101, 102, 103, 200, 201, 202, 203, 300, 301, 302, 303, 400, 401, 402, 403, 500, 501, 502, 503, 600, 601, 602, 603, 700, 701, 702, 703],
       [  4,   5,   6,   7, 104, 105, 106, 107, 204, 205, 206, 207, 304, 305, 306, 307, 404, 405, 406, 407, 504, 505, 506, 507, 604, 605, 606, 607, 704, 705, 706, 707],
       [  8,   9,  10,  11, 108, 109, 110, 111, 208, 209, 210, 211, 308, 309, 310, 311, 408, 409, 410, 411, 508, 509, 510, 511, 608, 609, 610, 611, 708, 709, 710, 711]])