raise ValueError("cannot reindex on an axis with duplicate labels") E ValueError: cannot reindex on an axis with duplicate labels

This error occurs when you try to reindex a pandas DataFrame or Series on an axis (rows or columns) that has duplicate labels. In other words, there are two or more rows or columns with the same label, and pandas cannot determine which one to keep.

To fix this error, you need to ensure that all labels on the axis are unique. You can do this by either:

1. Removing duplicate labels: You can use the `drop_duplicates()` method to remove duplicate labels from the DataFrame or Series. For example, `df.drop_duplicates(inplace=True)` will remove any rows with duplicate labels from the DataFrame `df`.

2. Renaming labels: If you have two or more labels that are the same, you can rename one or more of them to make them unique. You can use the `rename()` method to do this. For example, `df.rename(columns={'duplicate_label': 'new_label'}, inplace=True)` will rename the column with label `'duplicate_label'` to `'new_label'`.

Once you have made sure that all labels on the axis are unique, you can reindex the DataFrame or Series without encountering this error.