Using Julia, I'd like the find the period between two points in time, t2 and t1, where both t1 and t2 are in the format "y-m-d". I'm able to get this value in days, but I'd like to covert it to years:
date_format = DateFormat("y-m-d")
age_days = Date(t2, date_format) - Date(t1, date_format)
age_years = Dates.Year(age_days)
The above consistently returns an error. Understand I could just do Dates.value(age_days)/365.25, but is there a way to do this utilizing a built in function?
This functionality can be found in DayCounts.jl:
julia> using Dates, DayCounts
julia> d1=Date("2020-02-14", dateformat"y-m-d");
julia> d2=Date("2021-02-15", dateformat"y-m-d");
julia> yearfrac(d1,d2,DayCounts.ActualActualISDA())
1.003069091997904
The tricky part is to decide what to use as numerator and denominator when calculating such values. The above code used 2006 ISDA definitions, §4.16 (b) approach:
(# of days in standard year)/365 + (# of days in leap year)/366
There are many other implementations and they all seem to be implemented in that library.
Note that this is an additional answer to my previous post: Julia/Dates : convert a timespan from "days" to "year" or "Float64" that may be a better match here.