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fix(post-processing): flatten every index level #45263

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23de267
fix(post-processing): flatten every index level
Oct 13, 2026
fb3aef0
Merge branch 'master' into fix/flatten-multiindex
rusackas Oct 29, 2026
c520155
Merge branch 'master' into fix/flatten-multiindex
AliIbnBotir Oct 30, 2026
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3 changes: 2 additions & 1 deletion superset/utils/pandas_postprocessing/flatten.py
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Original file line number Diff line number Diff line change
Expand Up @@ -101,5 +101,6 @@ def flatten(
df.columns = _columns

if reset_index and not isinstance(df.index, pd.RangeIndex):
df = df.reset_index(level=0)
# every level of a MultiIndex, e.g. a pivot with several index columns
df = df.reset_index()

@codeant-ai-for-open-source codeant-ai-for-open-source Bot Oct 14, 2026

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Suggestion: When a later index level shares a name with a data column or another level, reset_index() raises ValueError, failing query post-processing.

Assessment: 🟠 Major · 🔁 Occurrence: Rarely · 🏷️ Logic error

Use CodeAnt Skill Fix in Cursor Fix in VSCode Claude

Prompt for AI Agent 🤖 
This is a comment left during a code review.

**Path:** superset/utils/pandas_postprocessing/flatten.py
**Line:** 105:105
**Comment:**
	*Logic Error: When a later index level shares a name with a data column or another level, `reset_index()` raises `ValueError`, failing query post-processing.

Validate the correctness of the flagged issue. If correct, How can I resolve this? If you propose a fix, implement it and please make it concise.
Once fix is implemented, also check other comments on the same PR, and ask user if the user wants to fix the rest of the comments as well. if said yes, then fetch all the comments validate the correctness and implement a minimal fix
👍 | 👎

@AliIbnBotir AliIbnBotir Oct 14, 2026

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Thanks. This collision isn’t new: the previous reset_index(level=0) already raises the same ValueError when level 0 shares a name with a column. This PR applies the same behaviour to every level instead of silently dropping levels 1..n. Happy to add explicit handling if maintainers prefer, but it seems out of scope for this fix.

@codeant-ai-for-open-source codeant-ai-for-open-source Bot Oct 14, 2026

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✅ Customized review instruction saved!

Instruction:

Do not flag reset_index() name-collision failures in flatten; level-0 collisions already had this behavior, and extending the reset to all levels is intentional in this change.

Applied to:

  • superset/utils/pandas_postprocessing/flatten.py

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return df
16 changes: 16 additions & 0 deletions tests/unit_tests/pandas_postprocessing/test_flatten.py
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Expand Up @@ -181,3 +181,19 @@ def test_escape_column_name():
"level1\\,value2" + FLAT_COLUMN_SEPARATOR + "level2\\, value2",
"level1\\,value3" + FLAT_COLUMN_SEPARATOR + "level2\\, value3",
]


def test_flat_should_reset_every_index_level():
index = pd.MultiIndex.from_arrays(
[["a", "a", "b"], [1, 2, 1]], names=["letter", "number"]
)
df = pd.DataFrame(index=index, data={"metric": [1, 2, 3]})
assert pp.flatten(df).equals(
pd.DataFrame(
{
"letter": ["a", "a", "b"],
"number": [1, 2, 1],
"metric": [1, 2, 3],
}
)
)
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