Florian - 8 months ago 22

Python Question

I want to add the previous n rows as columns to a numpy array. Here is an example:

`For n=2 this:`

[[ 1, 2]

[ 3, 4]

[ 5, 6]

[ 7, 8]

[ 9, 10]

[11, 12]]

Should be turned into this:

[[ 1, 2, 0, 0, 0, 0]

[ 3, 4, 1, 2, 0, 0]

[ 5, 6, 3, 4, 1, 2]

[ 7, 8, 5, 6, 3, 4]

[ 9, 10, 7, 8, 5, 6]

[11, 12, 9, 10, 7, 8]]

Any ideas how I could do that without going over the entire array in a loop.

Answer

Here is a way to pad 0 in the beginning of the array and then column stack them:

```
import numpy as np
n = 2
def mypad(myArr, n):
if n == 0:
return myArr
else:
return np.pad(myArr, ((n,0), (0,0)), mode = "constant")[:-n]
np.column_stack(mypad(arr, i) for i in range(n + 1))
# array([[ 1, 2, 0, 0, 0, 0],
# [ 3, 4, 1, 2, 0, 0],
# [ 5, 6, 3, 4, 1, 2],
# [ 7, 8, 5, 6, 3, 4],
# [ 9, 10, 7, 8, 5, 6],
# [11, 12, 9, 10, 7, 8]])
```