Extract Country

>>> from techminer2.fields.further_processing import extract_country
>>> extract_country( 
...     source="affiliations",
...     dest="countries_from_affiliations",
...     root_dir="example/",
... )

>>> # TEST:
>>> from techminer2.metrics import performance_metrics_frame
>>> performance_metrics( 
...     field='countries_from_affiliations',
...     metric='OCC',
...     top_n=10,
...     root_dir="example/",
... )

>>> from techminer2.fields import delete_field
>>> delete_field( 
...     field="countries_from_affiliations",
...     root_dir="example",
... )