How can columns be modified in bulk in pandas?

To batch modify column values in a Pandas DataFrame, you can use the following two methods:

1. use()

df['column_name'] = df['column_name'].apply(lambda x: 'new_value' if x == 'old_value' else x)

The above code replaces all instances of ‘old_value’ with ‘new_value’ in the column named ‘column_name’ in the dataframe df.

1. Make a substitution

df['column_name'].replace('old_value', 'new_value', inplace=True)

The code above replaces all occurrences of the ‘old_value’ in column ‘column_name’ in the dataframe df with the ‘new_value’. Setting inplace=True means the modification will be applied directly to the original dataframe.

Please replace ‘column_name’, ‘old_value’, and ‘new_value’ with the actual values in the above code.