Process a Field

>>> from techminer2.database.field_operators import TransformFieldOperator
>>> (
...     TransformFieldOperator()  
...     #
...     # FIELDS:
...     .with_field("author_keywords")
...     .with_other_field("author_keywords_copy")
...     #
...     # TRANSFORMATION:
...     .with_transformation(lambda x: x.str.lower())
...     #
...     # DATABASE:
...     .where_root_directory_is("example/")
...     #
...     .run()
... )