How to access columns after creating multiIndex

Question

I am making my DataFrame like this:

influenza_data = pd.DataFrame(data, columns = ['year', 'week', 'weekly_infections'])

and then I create MultiIndex from year and week columns:

influenza_data = influenza_data.set_index(['year', 'week'])

If I have MultiIndex my DataFrame looks like this:

          weekly_infections
year week                  
2009 40                6600
     41                7100
     42                7700
     43                8300
     44                8600
...                     ...
2019 10                8900
     11                6200
     12                5500
     13                3900
     14                3300

and data_influenza.columns:

Index(['weekly_infections'], dtype='object')

The problem I have is that I can't access year and week columns now.

If I try data_influenza['week'] or year I get KeyError: 'week'. I can only do data_influenza.weekly_infections and that returns a whole DataFrame

I know if I remove multiIndex I can easily access them but why can't I data_influenza.year or week with MultiIndex? I specified columns when I was creating Dataframe

you can access the multiindex with df.loc[2009,:] or df.query("year==2009") or df.query("year==2009 and week==40") ... there are a number of options. You can have a look here and here — sammywemmy
– sammywemmy, Commented Dec 2, 2020 at 4:57
@sammywemmy what would be equivalent of df['year'] to get whole year column? — cheshire
– cheshire, Commented Dec 2, 2020 at 5:01
not sure I understand. The year is already an index, so you should have all the years. — sammywemmy
– sammywemmy, Commented Dec 2, 2020 at 5:11
year was not an index, that's the thing that was confusing me. I posted my data_influenza.columns and it only shows Index(['weekly_infections'], dtype='object') so the only index I could work with was weakly_infections — cheshire
– cheshire, Commented Dec 2, 2020 at 14:54

Ehsan Tabatabaei · Accepted Answer · 2020-12-02 09:45:18Z

1

As Pandas documentation says here, you can access MultiIndex object levels by get_level_values(index) method:

influenza_data.index.get_level_values(0)    # year
influenza_data.index.get_level_values(1)    # week

Obviously, the index parameter represents the order of indices.

answered Dec 2, 2020 at 9:45

Ehsan Tabatabaei

1531 silver badge7 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to access columns after creating multiIndex

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related