Pandas: implementing Setting MultiIndex from Columns After Filtering Rows
I'm not sure how to approach I'm working with a DataFrame in Pandas 1.4.2 and I'm running into a question when trying to set a MultiIndex from columns after filtering the DataFrame based on a condition. Initially, I have a DataFrame that looks like this: ```python import pandas as pd data = { 'A': ['foo', 'bar', 'foo', 'bar', 'foo'], 'B': [1, 2, 3, 4, 5], 'C': [10, 20, 30, 40, 50] } df = pd.DataFrame(data) ``` After filtering rows where column 'B' is greater than 2, I expect to set columns 'A' and 'B' as a MultiIndex. Here’s what I tried: ```python df_filtered = df[df['B'] > 2] df_filtered.set_index(['A', 'B'], inplace=True) ``` However, I'm getting an unexpected behavior: `ValueError: Index has duplicates.` I checked the filtered DataFrame, and it appears to have unique values in the combination of columns 'A' and 'B', but upon setting the index, it raises this behavior. When I print the filtered DataFrame, I see the following: ```python print(df_filtered) ``` This shows the rows with 'B' values 3, 4, and 5, but there seem to be duplicates in the index. I’ve tried dropping duplicates explicitly using `df_filtered.drop_duplicates(subset=['A', 'B'], inplace=True)` before setting the index, but the behavior continues. I also checked the original DataFrame to make sure there are no duplicate combinations of 'A' and 'B' before filtering. What could be causing this scenario, and how can I successfully set a MultiIndex on my filtered DataFrame without working with this behavior? I'm working on a API that needs to handle this.