Last active
October 23, 2019 19:54
-
-
Save teoliphant/96eb779a16bd038e374f2703da62f06d to your computer and use it in GitHub Desktop.
Create a function to make a "sliding_window" output array from an input array and a rolling_window size.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import numpy as np | |
def array_for_sliding_window(x, wshape): | |
"""Build a sliding-window representation of x. | |
The last dimension(s) of the output array contain the data of | |
the specific window. The number of dimensions in the output is | |
twice that of the input. | |
Parameters | |
---------- | |
x : ndarray_like | |
An array for which is desired a representation to which sliding-windows | |
computations can be easily applied. | |
wshape : int or tuple | |
If an integer, then it is converted into a tuple of size given by the | |
number of dimensions of x with every element set to that integer. | |
If a tuple, then it should be the shape of the desired window-function | |
Returns | |
------- | |
out : ndarray | |
Return a zero-copy view of the data in x so that operations can be | |
performed over the last dimensions of this new array and be equivalent | |
to a sliding window calculation. The shape of out is 2*x.ndim with | |
the shape of the last nd dimensions equal to wshape while the shape | |
of the first n dimensions is found by subtracting the window shape | |
from the input shape and adding one in each dimension. This is | |
the number of "complete" blocks of shape wshape in x. | |
Raises | |
------ | |
ValueError | |
If the size of wshape is not x.ndim (unless wshape is an integer). | |
If one of the dimensions of wshape exceeds the input array. | |
Examples | |
-------- | |
>>> x = np.linspace(1,5,5) | |
>>> x | |
array([ 1., 2., 3., 4., 5.]) | |
>>> array_for_rolling_window(x, 3) | |
array([[ 1., 2., 3.], | |
[ 2., 3., 4.], | |
[ 3., 4., 5.]]) | |
>>> x = np.arange(1,17).reshape(4,4) | |
>>> x | |
array([[ 1, 2, 3, 4], | |
[ 5, 6, 7, 8], | |
[ 9, 10, 11, 12], | |
[13, 14, 15, 16]]) | |
>>> array_for_rolling_window(x, 3) | |
array([[[[ 1, 2, 3], | |
[ 5, 6, 7], | |
[ 9, 10, 11]], | |
[[ 2, 3, 4], | |
[ 6, 7, 8], | |
[10, 11, 12]]], | |
[[[ 5, 6, 7], | |
[ 9, 10, 11], | |
[13, 14, 15]], | |
[[ 6, 7, 8], | |
[10, 11, 12], | |
[14, 15, 16]]]]) | |
""" | |
x = np.asarray(x) | |
try: | |
nd = len(wshape) | |
except TypeError: | |
wshape = tuple(wshape for i in x.shape) | |
nd = len(wshape) | |
if nd != x.ndim: | |
raise ValueError("wshape has length {0} instead of " | |
"x.ndim which is {1}".format(len(wshape), x.ndim)) | |
out_shape = tuple(xi-wi+1 for xi, wi in zip(x.shape, wshape)) + wshape | |
if not all(i>0 for i in out_shape): | |
raise ValueError("wshape is bigger than input array along at " | |
"least one dimension") | |
out_strides = x.strides*2 | |
return np.lib.stride_tricks.as_strided(x, out_shape, out_strides) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Here to say thank you as well. Prior to this Gist, I was unaware of these
stride_tricks
methods.