def rolling_window(array, length):
"""Restride an array of shape (X_0, ... X_N) into an array of shape
(length, X_0 - length + 1, ... X_N) where each slice at index i along the
first axis is equivalent to result[i] = array[length * i:length * (i + 1)]
Parameters
----------
array : np.ndarray
The base array.
length : int
Length of the synthetic first axis to generate.
Returns
-------
out : np.ndarray
Example
-------
>>> from numpy import arange
>>> a = arange(25).reshape(5, 5)
>>> a
array([[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14],
[15, 16, 17, 18, 19],
[20, 21, 22, 23, 24]])
>>> rolling_window(a, 2)
array([[[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9]],
<BLANKLINE>
[[ 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14]],
<BLANKLINE>
[[10, 11, 12, 13, 14],
[15, 16, 17, 18, 19]],
<BLANKLINE>
[[15, 16, 17, 18, 19],
[20, 21, 22, 23, 24]]])
"""
orig_shape = array.shape
if not orig_shape:
raise IndexError("Can't restride a scalar.")
elif orig_shape[0] <= length:
raise IndexError(
"Can't restride array of shape {shape} with"
" a window length of {len}".format(
shape=orig_shape,
len=length,
)
)
num_windows = (orig_shape[0] - length + 1)
new_shape = (num_windows, length) + orig_shape[1:]
new_strides = (array.strides[0],) + array.strides
return np.lib.stride_tricks.as_strided(array, new_shape, new_strides)
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