zone-transitions

zone-transitions.R

library(clock)
library(purrr)
library(vctrs)
library(tibble)

generate_transitions <- function(zone,
                                 from = date_build(1900, 1, 1),
                                 to = date_build(2030, 1, 1)) {
  days <- date_seq(
    from = from,
    to = to,
    by = 1
  )
  
  days <- as_sys_time(days)
  info <- sys_time_info(days, zone = zone)
  
  # Must choose a unified transition time zone to use for display
  info$begin <- as_date_time(info$begin, zone = "UTC")
  info$end <- as_date_time(info$end, zone = "UTC")
  info$offset <- as.double(info$offset)
  
  info <- vec_unique(info)
  
  info
}

zones <- tzdb_names()
zones <- vec_set_names(zones, zones)

transitions <- map(zones, generate_transitions)
transitions <- list_rbind(transitions, names_to = "zone")
transitions <- as_tibble(transitions)

# All transitions (as long as more than one didn't happen within the same day)
transitions
#> # A tibble: 37,284 × 6
#>    zone             begin               end                 offset dst   abbre…¹
#>    <chr>            <dttm>              <dttm>               <dbl> <lgl> <chr>  
#>  1 Africa/Abidjan   -32767-01-01 00:00… 1912-01-01 00:16:08   -968 FALSE LMT    
#>  2 Africa/Abidjan   1912-01-01 00:16:08 32767-12-31 00:00:…      0 FALSE GMT    
#>  3 Africa/Accra     -32767-01-01 00:00… 1912-01-01 00:16:08   -968 FALSE LMT    
#>  4 Africa/Accra     1912-01-01 00:16:08 32767-12-31 00:00:…      0 FALSE GMT    
#>  5 Africa/Addis_Ab… -32767-01-01 00:00… 1908-04-30 21:32:44   8836 FALSE LMT    
#>  6 Africa/Addis_Ab… 1908-04-30 21:32:44 1928-06-30 21:30:00   9000 FALSE +0230  
#>  7 Africa/Addis_Ab… 1928-06-30 21:30:00 1930-01-04 21:00:00  10800 FALSE EAT    
#>  8 Africa/Addis_Ab… 1930-01-04 21:00:00 1936-12-31 21:30:00   9000 FALSE +0230  
#>  9 Africa/Addis_Ab… 1936-12-31 21:30:00 1942-07-31 21:15:00   9900 FALSE +0245  
#> 10 Africa/Addis_Ab… 1942-07-31 21:15:00 32767-12-31 00:00:…  10800 FALSE EAT    
#> # … with 37,274 more rows, and abbreviated variable name ¹​abbreviation

# Look just at the east coast in 2023
ny <- vec_slice(transitions, transitions$zone == "America/New_York") 
ny
#> # A tibble: 224 × 6
#>    zone             begin               end                 offset dst   abbre…¹
#>    <chr>            <dttm>              <dttm>               <dbl> <lgl> <chr>  
#>  1 America/New_York 1883-11-18 17:00:00 1918-03-31 07:00:00 -18000 FALSE EST    
#>  2 America/New_York 1918-03-31 07:00:00 1918-10-27 06:00:00 -14400 TRUE  EDT    
#>  3 America/New_York 1918-10-27 06:00:00 1919-03-30 07:00:00 -18000 FALSE EST    
#>  4 America/New_York 1919-03-30 07:00:00 1919-10-26 06:00:00 -14400 TRUE  EDT    
#>  5 America/New_York 1919-10-26 06:00:00 1920-01-01 05:00:00 -18000 FALSE EST    
#>  6 America/New_York 1920-01-01 05:00:00 1920-03-28 07:00:00 -18000 FALSE EST    
#>  7 America/New_York 1920-03-28 07:00:00 1920-10-31 06:00:00 -14400 TRUE  EDT    
#>  8 America/New_York 1920-10-31 06:00:00 1921-04-24 07:00:00 -18000 FALSE EST    
#>  9 America/New_York 1921-04-24 07:00:00 1921-09-25 06:00:00 -14400 TRUE  EDT    
#> 10 America/New_York 1921-09-25 06:00:00 1922-04-30 07:00:00 -18000 FALSE EST    
#> # … with 214 more rows, and abbreviated variable name ¹​abbreviation

# Now that we just have America/New_York rows, we can localize them
ny$begin <- date_set_zone(ny$begin, "America/New_York")
ny$end <- date_set_zone(ny$end, "America/New_York")

# 2023-03-12 03:00:00 is the one that just occurred
vec_slice(ny, get_year(ny$begin) == 2023 | get_year(ny$end) == 2023)
#> # A tibble: 3 × 6
#>   zone             begin               end                 offset dst   abbrev…¹
#>   <chr>            <dttm>              <dttm>               <dbl> <lgl> <chr>   
#> 1 America/New_York 2022-11-06 01:00:00 2023-03-12 03:00:00 -18000 FALSE EST     
#> 2 America/New_York 2023-03-12 03:00:00 2023-11-05 01:00:00 -14400 TRUE  EDT     
#> 3 America/New_York 2023-11-05 01:00:00 2024-03-10 03:00:00 -18000 FALSE EST     
#> # … with abbreviated variable name ¹​abbreviation