Pandas DataFrame の列にアクセスすると KeyError が発生するのはなぜですか?

Error: pandas HashTable KeyError

When attempting to print a specific column from a pandas DataFrame, you may encounter a KeyError if the requested column name does not exist in the DataFrame. This issue can arise due to several reasons, including hidden whitespace in column names or incorrect separator settings during CSV reading.

To investigate the issue further, first check the actual column names by printing the DataFrame's columns as a list:

print(reviews_new.columns.tolist())

Possible solutions include:

Whitespaces in Column Names:

• Strip whitespace from column names using reviews_new.columns = reviews_new.columns.str.strip().
• Alternatively, pass skipinitialspace=True to read_csv.

Incorrect Separator:

• Check the CSV file separator and pass the correct separator using sep parameter in read_csv. For example:

reviews_new = pd.read_csv("D:\\aviva.csv", sep=';')  # Semicolon separator
reviews_new = pd.read_csv("D:\\aviva.csv", sep='\s+')  # Whitespace separator

Absence of Column Name:

If the DataFrame does not have a column with the specified name, the error persists. To resolve this, select the first column by accessing the DataFrame's .index attribute. For example:

print(reviews_new.index.get_level_values('col1'))  # For MultiIndex

By following these steps, you can identify and resolve the cause of the KeyError and correctly access the desired column in your DataFrame.

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