randolf-scholz commented on issue #34890:
URL: https://github.com/apache/arrow/issues/34890#issuecomment-1531458999
One case when this bug appears in the wild is when trying to pivot a
`pandas.DataFrame` that has been loaded with the `pyarrow` backend:
```python
import pandas as pd
df = (
pd.DataFrame([("A", 1), ("B", 2), ("C", 3)], columns=["var", "val"])
.astype({"var": "string", "val": "float32"})
.astype({"var": "category", "val": "float32"})
)
# write and reload as parquet with pyarrow backend
df.to_parquet("demo.parquet")
df = pd.read_parquet("demo.parquet", dtype_backend="pyarrow")
print(df.dtypes) # var is now dictionary[int32,string]
df.pivot(columns=["var"], values=["val"]) # ✘ ArrowNotImplementedError
```
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