DataArray.mean
不保留取决于应用平均值的维度的坐标。
注:XLAT和XLONG不依赖于时间;然而,一些netcdf文件具有沿这两个方向的时间坐标。
我有这个netcdf文件wrfout_d03.nc,其中我用打开文件
ds = xr.open_dataset('/Users/jacob/Desktop/wrfpy/wrfout_d03_may.nc')
然后给出一个DataSet对象:
<xarray.Dataset>
Dimensions: (Time: 193, bio_emissions_dimension_stag: 41, bottom_top: 50, bottom_top_stag: 51, klevs_for_dvel: 1, seed_dim_stag: 12, soil_layers_stag: 4, south_north: 115, south_north_stag: 116, west_east: 115, west_east_stag: 116)
Coordinates:
XLAT (Time, south_north, west_east) float32 ...
XLONG (Time, south_north, west_east) float32 ...
XTIME (Time) datetime64[ns] ...
XLAT_U (Time, south_north, west_east_stag) float32 ...
XLONG_U (Time, south_north, west_east_stag) float32 ...
XLAT_V (Time, south_north_stag, west_east) float32 ...
XLONG_V (Time, south_north_stag, west_east) float32 ...
Dimensions without coordinates: Time, bio_emissions_dimension_stag, bottom_top, bottom_top_stag, klevs_for_dvel, seed_dim_stag, soil_layers_stag, south_north, south_north_stag, west_east, west_east_stag
Data variables:
datavars...
然后,我使用以下代码访问PM2_DRY变量:
pm25 = ds.PM2_5_DRY
生成的对象pm25的尺寸和坐标如下:
<xarray.DataArray 'PM2_5_DRY' (Time: 193, bottom_top: 50, south_north: 115, west_east: 115)>
[127621250 values with dtype=float32]
Coordinates:
XLAT (Time, south_north, west_east) float32 ...
XLONG (Time, south_north, west_east) float32 ...
XTIME (Time) datetime64[ns] ...
Dimensions without coordinates: Time, bottom_top, south_north, west_east
Attributes:
FieldType: 104
MemoryOrder: XYZ
description: pm2.5 aerosol dry mass
units: ug m^-3
stagger:
然后我操作pm25对象,并通过获得时间维度的平均值
pm25_mean = pm25.mean(dim='Time', keep_attrs = True)
生成的对象是一个DataArray,但没有坐标XLAT或XLON。
<xarray.DataArray 'PM2_5_DRY' (bottom_top: 50, south_north: 115, west_east: 115)>
array([[[14.73083 , 14.756626 , 14.796355 , ..., 20.325712 ,
20.855696 , 21.381271 ],
[14.651459 , 14.34477 , 14.371858 , ..., 18.00389 ,
18.4109 , 21.337002 ],
[14.59026 , 14.257076 , 14.293012 , ..., 17.391146 ,
18.217058 , 20.882664 ],
...,
[27.356459 , 27.21468 , 27.757051 , ..., 8.084272 ,
8.010168 , 7.989942 ],
[27.185486 , 27.02623 , 27.776043 , ..., 7.944748 ,
7.8795266 , 7.8552976 ],
[26.926008 , 27.724253 , 28.427626 , ..., 7.8269224 ,
7.773637 , 7.741844 ]],
Dimensions without coordinates: bottom_top, south_north, west_east
Attributes:
FieldType: 104
MemoryOrder: XYZ
description: pm2.5 aerosol dry mass
units: ug m^-3
stagger:
以下要检查的代码给出:
pm25_mean.coords
Coordinates:
*empty*
我试着在xarray中查看均值函数的文档;然而,我找不到任何选项来将坐标从以前的对象复制到新对象。
关于如何做到这一点,有什么建议吗?我想我需要从文件中访问这些坐标,然后再次组合它们。但我不知道该如何度过这个过程。
还有,这跟这个有关系吗?
XLAT (Time, south_north, west_east) float32
XLAT是一个多维坐标,它也依赖于时间。由于我得到了时间维度的平均值,维度pm25的数量从4减少到了3。这是否也会以某种方式影响坐标?
我需要最后一个物体有坐标XLAT和XLONG,因为我会可视化它。
谢谢你的帮助!
您只需要将坐标变量从三维转换为二维。
d = xr.open_dataset('.../pm25_sample.nc')
d['XLAT'] = d.XLAT.mean(dim = 'Time')
d['XLONG'] = d.XLONG.mean(dim = 'Time')
d['PM2_5_DRY'].mean(dim = 'Time')
...,
[ 0.03839084, 0.03837739, 0.03835952, ..., 0.03414929,
0.03412561, 0.03410038],
[ 0.03837854, 0.03836632, 0.03834687, ..., 0.03414606,
0.0341224 , 0.03409675],
[ 0.03836945, 0.03835024, 0.03833132, ..., 0.03414177,
0.03411727, 0.03409337]]], dtype=float32)
Coordinates:
XLAT (south_north, west_east) float32 14.086891 14.086907 ... 15.111996
XLONG (south_north, west_east) float32 120.49799 120.50717 ... 121.55791
Dimensions without coordinates: bottom_top, south_north, west_east
在xarray中似乎没有直接的解决方案(据我所知(,但我通过NCO找到了解决方案。
这来自这里的另一个帖子。这些是我为解决这个问题而采取的步骤。
首先,XLAT和XLONG没有出现在最终的DataArray中的原因是这些坐标取决于时间。
根据这个线程:在时间中设置坐标常数
- 我们必须获取NetCDF文件并分离感兴趣的变量(与时间相关(
- 我们在时间上平均出XLAT和XLONG,并将其放置在另一个nc文件中
- 我们将这两个文件附加在一起,以获得与时间无关的XLAT和XLONG
ncks -v variable input.nc variable.nc ncwa -a Time -v XLAT,XLONG input.nc latlon.nc ncks -A latlon.nc variable.nc
这样,当访问xarray中的文件并计算平均值时,我们得到以下DataArray:
<xarray.DataArray 'PM2_5_DRY' (bottom_top: 50, south_north: 115, west_east: 115)>
array([[[14.73083 , 14.756626 , 14.796355 , ..., 20.325712 ,
20.855696 , 21.381271 ],
[14.651459 , 14.34477 , 14.371858 , ..., 18.00389 ,
18.4109 , 21.337002 ],
[14.59026 , 14.257076 , 14.293012 , ..., 17.391146 ,
18.217058 , 20.882664 ],
...,
Coordinates:
XLAT (south_north, west_east) float32 ...
XLONG (south_north, west_east) float32 ...
Dimensions without coordinates: bottom_top, south_north, west_east
希望这也能帮助其他有同样问题的人!