多维Xarray滚动构造

问题描述

为多维滚动窗口具有xarray滚动构造的最佳方法是什么？这是一个小例子：

import numpy as np
from numpy.lib.stride_tricks import as_strided

data = np.array(np.arange(6).reshape(2,3),dtype="float64")


win_size = (
    3  # Size of the window (e.g. 3*3)
)
win_size_half = int(np.floor(win_size / 2))

# pad with nan to get correct window for the edges
data = np.pad(
    data,(win_size_half,win_size_half),"constant",constant_values=(np.nan),)

sub_shape = (win_size,win_size)
view_shape = tuple(np.subtract(data.shape,sub_shape) + 1) + sub_shape
data_view = as_strided(
    data,view_shape,data.strides * 2
)
data_view = data_view.reshape((-1,) + sub_shape)

#Expected results
>>> data_view
array([[[nan,nan,nan],[nan,0.,1.],3.,4.]],[[nan,[ 0.,1.,2.],[ 3.,4.,5.]],[ 1.,2.,[ 4.,5.,nan]],4.],[[ 0.,5.],[[ 1.,nan]]])

我想知道如何将xarray用于相同的目的。例如，使用xarray执行与上述相同的操作：

import xarray as xr

da =xr.DataArray(np.array(np.arange(6).reshape(2,dtype="float64"),dims=("a","b"))

# And something like
rolling = da.rolling({"a":win_size,"b":win_size})

# producing same results as in numpy example
rolling.construct("window_dim")

据我了解，xr.rolling不允许多个维度。请让我知道是否还有其他方法可以进行此类操作。

谢谢

解决方法

xr.rolling 现在接受多个维度。您必须提供一个 dict 映射（或基于关键字的）到rolling.construct。

您的 numpy 示例采用 windows 中心，它不是 xr.rolling 的默认值，因此您必须明确提供 center=True

以下代码给出与您的 numpy 代码相同的结果：

import xarray as xr
import numpy as np

da =xr.DataArray(np.array(np.arange(6).reshape(2,3),dtype="float64"),dims=("a","b"))

rolling = da.rolling({"a":3,"b":3},center=True)

# producing same results as in numpy example
da_roll = rolling.construct(a='ka',b='kb')
da_roll
Out[2]: 
<xarray.DataArray (a: 2,b: 3,ka: 3,kb: 3)>
array([[[[nan,nan,nan],[nan,0.,1.],3.,4.]],[[nan,[ 0.,1.,2.],[ 3.,4.,5.]],[ 1.,2.,[ 4.,5.,nan]]],[[[nan,4.],nan]],[[ 0.,5.],[[ 1.,nan]]]])
Dimensions without coordinates: a,b,ka,kb

numpy python python-xarray