Generalize stacking of array elements' neighbors into 3-D array

Question

Setup

Given a 2D array, I would like to create a 3D array where the values along the third dimension at (i.e. stacked[row, col, :]) are the flattened

Answer 1

This could be one approach -

import numpy as np

# Parameters
R = 3  # Radius
M1,N1 = padded.shape
rowlen = N1 - R + 1
collen = M1 - R + 1

# Linear indices for the starting R x R block
idx1 = np.arange(R)[:,None]*N1 + np.arange(R)

# Offset (from the starting block indices) linear indices for all the blocks
idx2 = np.arange(collen)[:,None]*N1 + np.arange(rowlen)

# Finally, get the linear indices for all blocks
all_idx = idx1.ravel()[None,None,:] + idx2[:,:,None]

# Index into padded for the final output
out = padded.ravel()[all_idx] 

Here's a sample run for radius, R = 4 -

In [259]: padded
Out[259]: 
array([[ 5,  5,  0,  3,  3,  3],
       [ 5,  5,  0,  3,  3,  3],
       [ 7,  7,  9,  3,  5,  5],
       [ 2,  2,  4,  7,  6,  6],
       [ 8,  8,  8, 10,  1,  1],
       [ 6,  6,  7,  7,  8,  8],
       [ 6,  6,  7,  7,  8,  8]])

In [260]: out
Out[260]: 
array([[[ 5,  5,  0,  3,  5,  5,  0,  3,  7,  7,  9,  3,  2,  2,  4,  7],
        [ 5,  0,  3,  3,  5,  0,  3,  3,  7,  9,  3,  5,  2,  4,  7,  6],
        [ 0,  3,  3,  3,  0,  3,  3,  3,  9,  3,  5,  5,  4,  7,  6,  6]],

       [[ 5,  5,  0,  3,  7,  7,  9,  3,  2,  2,  4,  7,  8,  8,  8, 10],
        [ 5,  0,  3,  3,  7,  9,  3,  5,  2,  4,  7,  6,  8,  8, 10,  1],
        [ 0,  3,  3,  3,  9,  3,  5,  5,  4,  7,  6,  6,  8, 10,  1,  1]],

       [[ 7,  7,  9,  3,  2,  2,  4,  7,  8,  8,  8, 10,  6,  6,  7,  7],
        [ 7,  9,  3,  5,  2,  4,  7,  6,  8,  8, 10,  1,  6,  7,  7,  8],
        [ 9,  3,  5,  5,  4,  7,  6,  6,  8, 10,  1,  1,  7,  7,  8,  8]],

       [[ 2,  2,  4,  7,  8,  8,  8, 10,  6,  6,  7,  7,  6,  6,  7,  7],
        [ 2,  4,  7,  6,  8,  8, 10,  1,  6,  7,  7,  8,  6,  7,  7,  8],
        [ 4,  7,  6,  6,  8, 10,  1,  1,  7,  7,  8,  8,  7,  7,  8,  8]]])