Return true if this DataFrame is in a materialized state, i.e. all information about the DataFrame’s values is encoded in self.base_node.
A DataFrame that’s freshly constructed with
from_pandas() will be in a materialized state. Operations on such
a DataFrame will change it to be not materialized. Calling
materialize() on a
non-materialized DataFrame will return a new DataFrame that is materialized.
A known problem is that DataFrames with ‘json_postgres’ columns are never in a materialized state, and cannot be materialized with materialize()
True if this DataFrame is in a materialized state, False otherwise