Adjust schema

The DataFrame interface has type argument T that doesn't affect the contents of DataFrame, but marks DataFrame with a type that represents the data schema that this DataFrame is supposed to have. This argument is used to generate extension properties for typed data access.

Another place where this argument has a special role is in interop with data classes:

• List<T>-> DataFrame<T>: toDataFrame

• DataFrame<T>-> List<T>: toList

Actual data in DataFrame may diverge from compile-time schema marker T due to dynamic nature of data inside DataFrame. However, at some points of code you may know exactly what DataFrame schema is expected. To match your knowledge with expected real-time DataFrame contents you can use one of two functions:

• cast — change type argument of DataFrame to the expected schema without changing data in DataFrame.

• convertTo — convert DataFrame contents to match the expected schema.