This S7 generic function defines the calendrical relationships between two
chronons, and is one of the building block for defining calendars in mixtime.
It calculates how many x chronons fit into the y chronon. Some chronon
sizes are context-dependent (such as the number of days in a month),
and so an optional time point defined in terms of y chronons can be
provided with at.
chronon_cardinality(x, y, ...)The primary time unit
The time unit to convert x into
Optional time point for context-dependent cardinality, defined in
terms of y (e.g., if y is tu_month(), then at could be a
yearmonth())
Numeric describing how many x time units fit into y at time at.
The methods are dispatched based on the shortest path along defined methods. This allows for defining only the direct relationships between adjacent time units, and relying on graph traversal to find how to convert between more distant units. For example the number of seconds in an hour can be calculated from the number of seconds in a minute and then number of minutes in an hour.
If a method is defined for converting between time units of different calendar systems (e.g., Gregorian calendar days to Chinese calendar days), then that method can be used to convert times at any granularity between the two systems.
# There are 12 months in a year
chronon_cardinality(tu_year(1L), tu_month(1L))
#> [1] 12
# There are 7 days in a week
chronon_cardinality(tu_week(1L), tu_day(1L))
#> [1] 7
# There are 3600 seconds in an hour
chronon_cardinality(tu_hour(1L), tu_second(1L))
#> Error in if (start == end) { return(start)}: missing value where TRUE/FALSE needed
# There are 18 "2 months" in 3 years
chronon_cardinality(tu_year(3L), tu_month(2L))
#> [1] 18
# There are 365 days in 2025 (a common year)
chronon_cardinality(tu_year(1L), tu_day(1L), at = year(as.Date("2025-01-01")))
#> Error in loadNamespace(x): there is no package called ‘vecvec’
# There are 366 days in 2024 (a leap year)
chronon_cardinality(tu_year(1L), tu_day(1L), at = year(as.Date("2024-01-01")))
#> Error in loadNamespace(x): there is no package called ‘vecvec’
# There are 29 days in February 2024 (a leap year)
chronon_cardinality(tu_month(1L), tu_day(1L), at = yearmonth(as.Date("2024-02-01")))
#> Error in loadNamespace(x): there is no package called ‘vecvec’