Pandas populate new dataframe column based on matching columns in another dataframe

Question

I have a df which contains my main data which has one million rows. My main data also has 30 columns. Now I want to add another column

Answer 1

You may try the following. It will merge both the datasets on specified column as key.

expected_result = pd.merge(df, df2, on = 'CATEGORY', how = 'left')