Invalidindexerror: reindexing only valid with uniquely valued index objects

InvalidIndexError: reindexing only valid with uniquely valued index objects

The error message “InvalidIndexError: reindexing only valid with uniquely valued index objects” occurs when you are trying to reindex a pandas DataFrame or Series with a non-unique index. In pandas, the index is used to label and identify the rows or elements of a DataFrame or Series.

When reindexing, pandas expects that the new index values should be unique, meaning that each value should only appear once in the index. If there are duplicate index values present, pandas cannot determine how to map or align the data properly, resulting in the “InvalidIndexError”.

Example

Let’s consider a simple example where we have a DataFrame with a non-unique index:

import pandas as pd

data = {'A': [1, 2, 3],
        'B': [4, 5, 6]}
df = pd.DataFrame(data, index=['a', 'b', 'a'])
  

In this example, the index of the DataFrame contains duplicate value ‘a’. If we try to reindex this DataFrame, it will raise an “InvalidIndexError”.

df.reindex(['a', 'b', 'c'])
  

To resolve this error, you need to ensure that the index values are unique. There are a few possible solutions:

1. Remove or replace duplicate index values.

df = df.loc[~df.index.duplicated(keep='first')]
    

2. Reset the index and create a new unique index.

df = df.reset_index(drop=True)
    

By ensuring a unique index, you can avoid the “InvalidIndexError” and successfully reindex your DataFrame or Series.