mlh3789 - 2 months ago 20

Python Question

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.]]

Answer Source

One option is

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

This is slightly wasteful due to the intermediate array but it's concise at least.