Add `nunique` reduction for number of unique values
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Description
Is your feature request related to a problem?
From https://github.com/pydata/xarray/issues/9544#issuecomment-2372685411
Though perhaps we should add nunique along a dimension implemented as sort along axis, succeeding-elements-are-not-equal along axis handling NaNs, then sum along axis.
xref pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.nunique.html
I think I'd add it to https://github.com/pydata/xarray/blob/main/xarray/util/generate_aggregations.py
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reading xarray/util/generate_aggregations.py and the existing reduction definitions it generates. Confirm how reductions handle dimensions and NaNs, then add the nunique reduction following the issue's described behavior. Done means xarray exposes a number-of-unique-values reduction along a dimension.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- data
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100