What causes \"ValueError: cannot reindex from a duplicate axis\" error in Python pandas?

Understanding "ValueError: cannot reindex from a duplicate axis"

In Python pandas, the "ValueError: cannot reindex from a duplicate axis" error occurs when trying to assign or join a column or row to a DataFrame with duplicate values in the specified axis. This error message indicates that the operation cannot be performed because the resulting DataFrame would have duplicate index values along the specified axis.

Problem Context

In the provided context, the error arises when attempting to create a row in the affinity_matrix DataFrame with the name 'sums' and assigning it the sum of all columns. However, the error message suggests that there may be duplicate values in the DataFrame's columns.

To resolve this issue, we need to check if there are duplicate values in affinity_matrix.columns. Here is an example snippet for checking:

<code class="python">import pandas as pd

# Get the columns of the DataFrame
columns = affinity_matrix.columns

# Find duplicate column names
duplicates = columns[columns.duplicated()]

# Print the duplicate column names
print("Duplicate column names:", duplicates)</code>

If the output shows any duplicate column names, then they need to be removed or renamed before attempting to assign the 'sums' row.

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