Section: 15.1 What are Groups?

15.1 What are Groups?

NetCDF-4 files can organize variables, dimensions, and attributes in hierarchical groups.

Groups are like directories in a file system, except they are all within a file.
When using groups, the "ncid" becomes the ID of the file and the group within that file. That is, different groups in the same file will have different ncids.
Every file contains at least the root group. The ncid of the root groups is returned on an open or create.
Groups (other than the root group) are part of the enhanced model. Using groups means that no existing netCDF software (except ncdump) will be able to read the file.
Dimensions are scoped such that they can be seen in all child groups.
A global attribute is now global to the group, not the file.
To read enhanced model netCDF-4 files in a general way, recursion is required.
Use of Groups is optional, with backward compatibility maintained by putting everything in the top-level unnamed Group.
Unlike HDF5, netCDF-4 requires that Groups form a strict hierarchy.