如何在netCDF文件中按维度筛选数据

Question

使用python，我已经使用netCDF4库导入了一个netCDF文件

import netCDF4 as nc
ncObject = nc.Dataset('somefile.nc')

以下是ncObject的维度

fov(9)
y(100)
x(100)
pressure(100)
cloud_layers(2)

我试图做的是按维度或维度系列过滤数据集。所以基本上我希望我的新ncObject只包括fov=0和cloud\u layers=0的记录。我知道这可以通过使用xarray模块和下面看到的代码来完成，但我想使用netCDF4包做同样的事情（原因是netCDF4可以更好地访问组文件夹中的嵌套变量）

ncObjectNew = ncObject.sel(cloud_layers=0).sel(fov=0)

好奇是否有人知道如何使用netCDF4符号/语法编写上述内容

提前感谢您提供的任何帮助

杰夫

Answer 1

这个make_subsets函数应该可以帮助您：

import netCDF4 as nc

def make_subsets(variables, ranges):
    """
    Inputs:
      variables: dict with key: var name, value: netCDF variable
      ranges: dict with key: dim name, value: 2-tuple of (start, stop) indices
    Returns:
      variables subsetted according to the supplied ranges, in same format as 
      the input variables dictionary
    """
    subsets = {}
    for varname, v in variables.items():
        subset_args = []
        if v.shape:
            for size, dim in zip(v.shape, v.dimensions):
                if dim in ranges:
                    subset_args.append(slice(*ranges[dim]))
                else:
                    subset_args.append(slice(0, size))
            print(subset_args)
            subsets[varname] = v.__getitem__(subset_args)
        else:
            # scalar                                                                                
            subsets[varname] = v
    return subsets


ncObject = nc.Dataset('somefile.nc')

# start and end values for every dimension we want to subset                                        
# (as usual, end value is the index AFTER the last element wanted)                                  
ranges = {'fov': (0, 1), 'cloud_layers': (0, 1)}

subsets = make_subsets(ncObject.variables, ranges)

for varname, v in subsets.items():
    print(varname, v.shape)