BUG: Some str reducers fail in Groupby.transform with axis=1 · Issue #45986 · pandas-dev/pandas (original) (raw)

All raise a ValueError when used with axis=1, e.g.

df = DataFrame({"a": [1, 2], "b": [3, 4], "c": [5, 6]}, index=["x", "y"])
result = df.groupby([0, 0, 1], axis=1).transform("first")