如何访问 Python 中 xarray.Dataset 的绑定方法 mapping.values 的数据变量值

Question

如何访问 xarray.Dataset 的绑定方法 mapping.values 的数据变量值，正确的语法是什么：

我需要检索 pm2p5_conc 数据变量：

pmScatter["pm25"].values

array([<bound method Mapping.values of <xarray.Dataset>
Dimensions:     ()
Coordinates:
    level       float32 0.0
    time        timedelta64[ns] 00:00:00
    longitude   float64 2.352
    latitude    float64 48.86
Data variables:
    pm2p5_conc  float64 26.23
Attributes:
    title:        PM25 Air Pollutant FORECAST at 8 levels
    institution:  Data produced by Meteo France
    source:       Data from ENSEMBLE model
    history:      Model ENSEMBLE FORECAST
    FORECAST:     Europe, 20210325-20210327+[0H_0H]
    summary:      ENSEMBLE model hourly FORECAST of PM25 concentration at 8 l...
    project:      MACC-RAQ (http://macc-raq.gmes-atmosphere.eu)>,
       <bound method Mapping.values of <xarray.Dataset>

数据变量 pm2p5_conc

按照 dl.meteos 的建议，我得到一个关键错误：

    def normalize(x):
        return 0.5 + (x - x.min()) / (x.max() - x.min())

risk = normalize(pmScatter["pm25"]["pm2p5_conc"].values)* pop.pop_2010[::resolution].values * normalize(covidExtra.hosp[::resolution].values) gives me the following error:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-14-47c4a255de66> in <module>
----> 1 risk = normalize(pmScatter["pm25"]["pm2p5_conc"].values)* pop.pop_2010[::resolution].values * normalize(covidExtra.hosp[::resolution].values)
      2 risk = np.vstack((x,y,risk)).T
      3 risk = pd.DataFrame(risk,columns=['lon','lat','risk'])
      4 

~/.pyenv/versions/lewagon/lib/python3.8/site-packages/pandas/core/series.py in __getitem__(self, key)
    851 
    852         elif key_is_scalar:
--> 853             return self._get_value(key)
    854 
    855         if is_hashable(key):

~/.pyenv/versions/lewagon/lib/python3.8/site-packages/pandas/core/series.py in _get_value(self, label, takeable)
    959 
    960         # Similar to Index.get_value, but we do not fall back to positional
--> 961         loc = self.index.get_loc(label)
    962         return self.index._get_values_for_loc(self, loc, label)
    963 

~/.pyenv/versions/lewagon/lib/python3.8/site-packages/pandas/core/indexes/range.py in get_loc(self, key, method, tolerance)
    352                 except ValueError as err:
    353                     raise KeyError(key) from err
--> 354             raise KeyError(key)
    355         return super().get_loc(key, method=method, tolerance=tolerance)
    356 

KeyError: 'pm2p5_conc'

Answer 1

您正在使用 values 方法访问xarray.Dataset ，该方法产生类型转换以恢复 numpy 数组。

解决方案很简单：

pmScatter["pm25"]["pm2p5_conc"].values

在.values上调用xarray.DataArray 。 请查看 xarray 文档以了解DataArray和Dataset之间的区别。