sliding window of M-by-N shape numpy.ndarray

Question

I have a numpy array of shape (6,2)

[[00,01],
 [10,11],
 [20,21],
 [30,31],
 [40,41],
 [50,51]]

I need a sliding window with step size 1 an

Answer 1

In [1]: import numpy as np

In [2]: a = np.array([[00,01], [10,11], [20,21], [30,31], [40,41], [50,51]])

In [3]: w = np.hstack((a[:-2],a[1:-1],a[2:]))

In [4]: w
Out[4]: 
array([[ 0,  1, 10, 11, 20, 21],
       [10, 11, 20, 21, 30, 31],
       [20, 21, 30, 31, 40, 41],
       [30, 31, 40, 41, 50, 51]])

You could write this in as a function as so:

def window_stack(a, stepsize=1, width=3):
    n = a.shape[0]
    return np.hstack( a[i:1+n+i-width:stepsize] for i in range(0,width) )

---

This doesn't really depend on the shape of the original array, as long as a.ndim = 2. Note that I never use either lengths in the interactive version. The second dimension of the shape is irrelevant; each row can be as long as you want. Thanks to @Jaime's suggestion, you can do it without checking the shape at all:

def window_stack(a, stepsize=1, width=3):
    return np.hstack( a[i:1+i-width or None:stepsize] for i in range(0,width) )