Add column to pandas dataframe indexed by another column

Question

I have a pandas dataframe that looks like

        some_data  another_id
id                                                            
312871     ...     abc
312977     ...     def
...

and a dictionary letters = {"abc": "x", "def": "y"}. I want to add letters as a column to my dataframe, but it is morally indexed by another_id so I can't just set df["letters"] = letters.

I'm sure there's a beautiful, elegant way to do this. What is it?

Answer 1

I hope i understand your question correct. Do you want something like:

df['letters'] = df['another_id'].map(letters)

        some_data another_id letters
id                                  
312871          5        abc       x
312977          6        def       y

Answer 2

Aha!

df.merge(pd.DataFrame({"letters": letters}), left_on="dscode", right_index=True)