Panoramasx opened a new issue, #45208:
URL: https://github.com/apache/superset/issues/45208
### Bug description
The `rank` post-processing operation ignores `group_by=""`, even when the
DataFrame has a column with that name. It computes a global percentile rank
instead of ranking within each group.
An empty string is a valid pandas column label. `group_by` is typed as `str
| None`, and `None` already represents an unspecified grouping column. The
truthiness check in `superset/utils/pandas_postprocessing/rank.py` treats both
values alike.
### How to reproduce the bug
Run this in a Superset development environment:
```python
import pandas as pd
from superset.utils import pandas_postprocessing as pp
df = pd.DataFrame({"": ["A", "A", "B", "B"], "value": [1, 3, 2, 4]})
print(pp.rank(df.copy(), "value", group_by="")["rank"].tolist())
# Actual: [0.25, 0.75, 0.5, 1.0]
print(df.groupby("")["value"].rank(pct=True).tolist())
# Expected: [0.5, 1.0, 0.5, 1.0]
```
The same group values under a non-empty column name produce the expected
group-wise ranks. Omitting `group_by` or passing `None` should continue to
compute global ranks.
### Screenshots/recordings
Not applicable: this reproduction exercises a backend DataFrame operation.
### Superset version
master / latest-dev, commit `42bbfa49079eff910ead01b7880b94d09c5ca520`
### Python version
3.12.14
### Node version
Not applicable
### Browser
Not applicable
### Additional context
Verified with pandas 2.3.3 in the project's pytest environment. The minimal
fix is to check `group_by is not None` rather than its truthiness. A regression
test covers an empty-string column label, an ordinary label, and explicit
`None`; existing tests cover omitted grouping and a single group.
I have prepared a fix and tests for this issue.
### Checklist
- [ ] I have searched Superset docs and Slack and didn't find a solution to
my problem.
- [x] I have searched the GitHub issue tracker and didn't find a similar bug
report.
- [x] I have checked Superset's logs for errors and if I found a relevant
Python stacktrace, I included it here as text in the "additional context"
section.
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