mlh3789 - 2 months ago 20
Python Question

# Quick way to upsample numpy array by nearest neighbor tiling

I have a 2D array of integers that is MxN, and I would like to expand the array to (BM)x(BN) where B is the length of a square tile side thus each element of the input array is repeated as a BxB block in the final array. Below is an example with a nested for loop. Is there a quicker/builtin way?

``````import numpy as np

a = np.arange(9).reshape([3,3])            # input array - 3x3
B=2.                                       # block size - 2
A = np.zeros([a.shape[0]*B,a.shape[1]*B])  # output array - 6x6

# Loop, filling A with tiled values of a at each index
for i,l in enumerate(a):                   # lines in a
for j,aij in enumerate(l):             # a[i,j]
A[B*i:B*(i+1),B*j:B*(j+1)] = aij
``````

Result ...

``````a=      [[0 1 2]
[3 4 5]
[6 7 8]]

A =     [[ 0.  0.  1.  1.  2.  2.]
[ 0.  0.  1.  1.  2.  2.]
[ 3.  3.  4.  4.  5.  5.]
[ 3.  3.  4.  4.  5.  5.]
[ 6.  6.  7.  7.  8.  8.]
[ 6.  6.  7.  7.  8.  8.]]
``````

``````>>> a.repeat(2, axis=0).repeat(2, axis=1)