Signature Description

enum class time_frequency : unsigned char  {
    annual = 1,
    monthly = 2,
    weekly = 3,
    daily = 4,
    hourly = 5,
    minutely = 6,
    secondly = 7,
    millisecondly = 8,
    // microsecondly = 9,
    // nanosecondly = 10
}; 
        
This enum specifies time frequency for index generation and otherwise. The names are self-explanatory.
C++ DataFrame