为什么分配'xr。对数据集变量更改不相关的坐标?

当我分配 xr.ones_like 对于数据集变量,我丢失了一些分配给坐标的数据:

import xarray as xr
import numpy as np

A, B, C = 2, 3, 4

ds = xr.Dataset()
ds.coords['source'] = (['a', 'b', 'c'], np.random.random((A, B, C)))
ds.coords['unrelated'] = (['a', 'c'], np.random.random((A, C)))

print('INITIAL:', ds['unrelated'], '\n')

# do 'ones_like' manually
ds['dest-1'] = (['a', 'b'], np.ones((A, B)))

print('AFTER dest-1:', ds['unrelated'], '\n')

ds['dest-2'] = xr.ones_like(ds['source'].isel(c=0))

print('AFTER dest-2:', ds['unrelated'], '\n')

输出:

INITIAL: <xarray.DataArray 'unrelated' (a: 2, c: 4)>
array([[0.185851, 0.962589, 0.772985, 0.570292],
       [0.905792, 0.865125, 0.412361, 0.666977]])
Coordinates:
    unrelated  (a, c) float64 0.1859 0.9626 0.773 0.5703 0.9058 0.8651 ...
Dimensions without coordinates: a, c

AFTER dest-1: <xarray.DataArray 'unrelated' (a: 2, c: 4)>
array([[0.185851, 0.962589, 0.772985, 0.570292],
       [0.905792, 0.865125, 0.412361, 0.666977]])
Coordinates:
    unrelated  (a, c) float64 0.1859 0.9626 0.773 0.5703 0.9058 0.8651 ...
Dimensions without coordinates: a, c

AFTER dest-2: <xarray.DataArray 'unrelated' (a: 2)>
array([0.185851, 0.905792])
Coordinates:
    unrelated  (a) float64 0.1859 0.9058
Dimensions without coordinates: a

为什么 unrelated 使用后丢失维度 xr。ones\u喜欢 ?