# InvalidIndexError: Reindexing only valid with uniquely valued Index objects

- **ID:** `python/pandas-invalidindex-on-reset`
- **Domain:** python
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

An operation like reindex, join, or merge on axis=0 hit duplicate index labels. Common after concat of frames that each carry their own index.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   df = df.reset_index(drop=True) before reindex/merge
   ```
2. **** (90% success)
   ```
   df = df[~df.index.duplicated(keep='first')]
   ```

## Dead Ends

- **** — Sorting doesn't remove duplicates (85% fail)
- **** — Still requires unique index (90% fail)