issue_comments: 457874348
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html_url | issue_url | id | node_id | user | created_at | updated_at | author_association | body | reactions | performed_via_github_app | issue |
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https://github.com/pydata/xarray/issues/1475#issuecomment-457874348 | https://api.github.com/repos/pydata/xarray/issues/1475 | 457874348 | MDEyOklzc3VlQ29tbWVudDQ1Nzg3NDM0OA== | 1217238 | 2019-01-26T23:14:18Z | 2019-01-26T23:14:18Z | MEMBER |
The long term plan in https://github.com/pydata/xarray/issues/1603 ("Explicit indexes") is to eliminate this distinction -- we'll simply have variables, which can be in the form of data variables or coordinates, and indexes, for look-up along any coordinate.
I understand (N+1) sized coordinates for quad-mesh geometries, where N is the number of physical dimensions. I'm not sure I understand (N,M) sized coordinates for unstructured meshes -- what is M here? The total number of cells? Some arbitrary constant indicating the maximum number of sides for a single cell? I do. Logically I see two approaches here: 1. Putting cell bounds into structured dtypes, and adding sugar to make these easier to use (as discussed in https://github.com/pydata/xarray/issues/1475#issuecomment-314844258). 2. Putting cell bounds directly into xarray's data model in some form, so we can deviate from our current rule that "coordinates dimensions must be a subset of DataArray dimensions." (1) feels like the safe approach (from xarray's perpsective). Maybe structured dtypes too annoying to use on a routine basis, but there also are other use cases for them that would benefit from some attention. I worry that solutions in the style of (2) would bake domain specific logic deep into xarray's data model and make the whole library more complex, though I do appreciate that cell bounds are a pretty ubiquitous concept for modeling physical phenomena. One way of solving (2) would be to allow something like "isolated" or "non-aligned" dimensions, which aren't shared across a Dataset/DataArray and are allowed to deviate on a per-variable basis. |
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