Keys are structural columns that other operations reference. There is one key
per type; re-registering a type replaces it.
Usage
add_key(sfw, name, type, var)
get_keys(sfw)
Arguments
- sfw
A sample frame.
- name
Human-readable key name.
- type
Key role: "entity", "time", "unique_record" (or a custom
role).
- var
The column name.
Value
The updated sample frame.