I am encountering some odd behavior in pandas, and I am hoping someone could shed some light on specifics from the df.assign(...) function in a pandas dataframe. I am getting a ValueError when trying to assign to column, despite the function being valid. def is_toc_row(row): m_sig = m_df.loc[m_df.signature == row.signature] pct = (~pd.isnull(m_sig.line_type)).sum() / m_sig.shape[0] return (not pd.isnull(row.line_type)) or (pct < .5) m_df = m_df.assign(is_toc_row=is_toc_row) Gives: ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all(). But this works totally fine: for ind, row in m_df.iterrows(): m_df.at[ind, 'is_toc_row'] = is_toc_row(row) Is there some issue with referencing the rest of the DataFrame in the function? All I see in the docs is that the subject df cannot change, which it does not. Of course I am capable of building a workaround, I just want to understand why this does not work for future use. Continue reading...
