Here’s one leveraging np.lib.stride_tricks.as_strided
–
def random_windows_per_row_strided(arr, W=3):
idx = np.random.randint(0,arr.shape[1]-W+1, arr.shape[0])
strided = np.lib.stride_tricks.as_strided
m,n = arr.shape
s0,s1 = arr.strides
windows = strided(arr, shape=(m,n-W+1,W), strides=(s0,s1,s1))
return windows[np.arange(len(idx)), idx]
Runtime test on bigger array with 10,000
rows –
In [469]: arr = np.random.rand(100000,100)
# @Psidom's soln
In [470]: %timeit select_random_windows(arr, window_size=3)
100 loops, best of 3: 7.41 ms per loop
In [471]: %timeit random_windows_per_row_strided(arr, W=3)
100 loops, best of 3: 6.84 ms per loop
# @Psidom's soln
In [472]: %timeit select_random_windows(arr, window_size=30)
10 loops, best of 3: 26.8 ms per loop
In [473]: %timeit random_windows_per_row_strided(arr, W=30)
100 loops, best of 3: 9.65 ms per loop
# @Psidom's soln
In [474]: %timeit select_random_windows(arr, window_size=50)
10 loops, best of 3: 41.8 ms per loop
In [475]: %timeit random_windows_per_row_strided(arr, W=50)
100 loops, best of 3: 10 ms per loop