python - xarray 将新的二维坐标设置为维度

Question

我在 x/y 网格上有一个海面温度值的 xarray 数据集。x并且y是一维向量坐标，所以它看起来像这个最小的例子：

<xarray.Dataset>
Dimensions:  (x: 10, y: 10)
Coordinates:
  * x        (x) int64 0 1 2 3 4 5 6 7 8 9
  * y        (y) int64 0 1 2 3 4 5 6 7 8 9
Data variables:
    data     (x, y) float64 0.559 0.01037 0.1562 ... 0.08778 0.3272 0.8661

我能够从这个 x/y 网格计算纬度/经度，输出是 2 个二维数组。我可以将它们添加为坐标ds.assign_coords：

<xarray.Dataset>
Dimensions:  (x: 10, y: 10)
Coordinates:
  * x        (x) int64 0 1 2 3 4 5 6 7 8 9
  * y        (y) int64 0 1 2 3 4 5 6 7 8 9
    lat      (x, y) float64 30.0 30.0 30.0 30.0 30.0 ... 39.0 39.0 39.0 39.0
    lon      (x, y) float64 -120.0 -119.0 -118.0 -117.0 ... -113.0 -112.0 -111.0
Data variables:
    data     (x, y) float64 0.559 0.01037 0.1562 ... 0.08778 0.3272 0.8661

但我想.sel沿着纬度/经度的切片。这目前是不可能的，因为我得到了错误：

ds.sel(lat=slice(32,36), lon=slice(-118, -115))

ValueError                                Traceback (most recent call last)
<ipython-input-20-28c79202d5f3> in <module>
----> 1 ds.sel(lat=slice(32,36), lon=slice(-118, -115))

~/.local/lib/python3.8/site-packages/xarray/core/dataset.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
   2363         """
   2364         indexers = either_dict_or_kwargs(indexers, indexers_kwargs, "sel")
-> 2365         pos_indexers, new_indexes = remap_label_indexers(
   2366             self, indexers=indexers, method=method, tolerance=tolerance
   2367         )

~/.local/lib/python3.8/site-packages/xarray/core/coordinates.py in remap_label_indexers(obj, indexers, method, tolerance, **indexers_kwargs)
    419     }
    420 
--> 421     pos_indexers, new_indexes = indexing.remap_label_indexers(
    422         obj, v_indexers, method=method, tolerance=tolerance
    423     )

~/.local/lib/python3.8/site-packages/xarray/core/indexing.py in remap_label_indexers(data_obj, indexers, method, tolerance)
    256     new_indexes = {}
    257 
--> 258     dim_indexers = get_dim_indexers(data_obj, indexers)
    259     for dim, label in dim_indexers.items():
    260         try:

~/.local/lib/python3.8/site-packages/xarray/core/indexing.py in get_dim_indexers(data_obj, indexers)
    222     ]
    223     if invalid:
--> 224         raise ValueError(f"dimensions or multi-index levels {invalid!r} do not exist")
    225 
    226     level_indexers = defaultdict(dict)

ValueError: dimensions or multi-index levels ['lat', 'lon'] do not exist

所以我的问题是：如何更改 to 的尺寸data而(lon: (10,10), lat: (10,10))不是(x: 10, y: 10？这甚至可能吗？

重现示例数据集的代码：

import numpy as np
import xarray as xr

# Create sample data
data = np.random.rand(10,10)
x = y = np.arange(10)

# Set up dataset
ds = xr.Dataset(
    data_vars = dict(
        data = (["x", "y"], data)
    ),
    coords= {
        "x" : x,
        "y" : y
    }
)

# Create example lat/lon and assign to dataset
lon, lat = np.meshgrid(np.linspace(-120, -111, 10), np.linspace(30, 39, 10))

ds = ds.assign_coords({
    "lat": (["x", "y"], lat),
    "lon": (["x", "y"], lon)
})

标签： pythonnumpypython-xarray