era v0.6.0 is now available on CRAN:

install.packages("era")
library(era)

This minor release adds functions for chronological comparison of year vectors:

x <- yr(c(200, 100, 300), "BCE")
yr_earlier_than(x, yr(150, "BCE"))
#> # BCE years <yr_lgl[3]>:
#> [1] FALSE FALSE  TRUE
#> # Era: Before Common Era (BCE): Gregorian years (365.2425 days), counted backwards from 1

yr_later_than(x, yr(150, "BCE"))
#> # BCE years <yr_lgl[3]>:
#> [1]  TRUE FALSE FALSE
#> # Era: Before Common Era (BCE): Gregorian years (365.2425 days), counted backwards from 1

And for calculating chronological differences between year vectors:

yr_difference(yr(300, "BCE"), yr(100, "BCE"))
#> # years <yr[1]>:
#> [1] 200
#> # Era: Gregorian years (365.2425 days)

These functions are aware of era directionality: “BCE” years count backwards, so 300 BCE is earlier than 100 BCE. They support work on tempo, a new package I am working on that represents chronological intervals and the temporal relations between them.

Links

• era on CRAN
• era package documentation
• Introductory vignette
• Source code (GitHub)