10.3.2 Setting the index

The default index of a dataframe is the row numbers. These are generated automatically when a dataframe is created and no index is specified. Here is an example.

We create a dataframe from a list of lists:

towns=[['Stockholm', 'Sweden', 188,975904],
       ['Malmö', 'Sweden', 322, 316588],
       ['Oslo', 'Norway', 481, 693491],
       ['Bergen', 'Norway', 464, 28392]]
town=pd.DataFrame(towns, columns=['City','Country','area','population'])

This produces a dataframe with rows labeled by their row numbers:

        City Country  area  population
0  Stockholm  Sweden   188      975904
1      Malmö  Sweden   322      316588
2       Oslo  Norway   481      693491
3     Bergen  Norway   464      28392

We can change this by choosing a column to be the index. The column can be duplicated—one serving as the index and the other belonging to the...