I have a numpy array. I need a rolling window:
[1,2,3,4,5,6]
expected result for sub array length 3:
[1,2,3] [2,3,4] [3,4,5] [4,5,6]
Could you please help. I am not a python dev.
Python 3.5
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2 Answers
If numpy is not a necessity, you can just use a list comprehension. If x is your array, then:
In [102]: [x[i: i + 3] for i in range(len(x) - 2)]
Out[102]: [[1, 2, 3], [2, 3, 4], [3, 4, 5], [4, 5, 6]]
Alternatively, using np.lib.stride_tricks. Define a function rolling_window (source from this blog):
def rolling_window(a, window):
shape = a.shape[:-1] + (a.shape[-1] - window + 1, window)
strides = a.strides + (a.strides[-1],)
return np.lib.stride_tricks.as_strided(a, shape=shape, strides=strides)
Call the function with window=3:
In [122]: rolling_window(x, 3)
Out[122]:
array([[1, 2, 3],
[2, 3, 4],
[3, 4, 5],
[4, 5, 6]])
Comments
This might also be interesting: The view_as_windows() function from the skimage.util module. It returns a
rolling window view of the input n-dimensional array.
Source: https://scikit-image.org/docs/dev/api/skimage.util.html#skimage.util.view_as_windows
Directly from the linked examples (adapted for your range of numbers):
>>> import numpy as np
>>> from skimage.util import view_as_windows
>>>
>>> A = np.arange(1,7)
>>> A
array([1, 2, 3, 4, 5, 6])
>>> window_shape = (3,)
>>> B = view_as_windows(A, window_shape)
>>> B.shape
(4, 3)
>>> for win in B:
print(win)
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
[4, 5, 6]
