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December 6, 2021 20:08
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Calculating UTC midnight during standard and DST
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#;; Find the local midnight time in UTC for a given timezone | |
library(tidyverse) | |
library(lubridate) | |
library(glue) | |
# tgtTimezone <- "America/Chicago" | |
# tgtTimezone <- "America/Sao_Paulo" | |
# tgtYear <- 2021 | |
# | |
# tibble(utc_dt = seq(ymd_hms(glue("{tgtYear}-01-01T00:00:00Z")), | |
# ymd_hms(glue("{tgtYear + 1}-01-01T00:00:00Z")), | |
# by="hour")) %>% | |
# mutate(local_dt = with_tz(utc_dt, tgtTimezone), | |
# utcLocalMidnightOffset = glue("{as_date(local_dt) + 1}T00:00:00") %>% | |
# ymd_hms(tz=tgtTimezone) %>% | |
# with_tz(tz="UTC") %>% | |
# hour()) %>% | |
# filter((utcLocalMidnightOffset != lag(utcLocalMidnightOffset)) | (row_number() == 1)) | |
getMidnightDSTUTC <- function(tgtTimezone, tgtYear=year(now())) { | |
tibble(utc_dt = seq(ymd_hms(glue("{tgtYear}-01-01T00:00:00Z")), | |
ymd_hms(glue("{tgtYear + 1}-01-01T00:00:00Z")), | |
by="hour")) %>% | |
mutate(local_dt = with_tz(utc_dt, tgtTimezone), | |
utcLocalMidnight = glue("{as_date(local_dt) + 1}T00:00:00") %>% | |
ymd_hms(tz=tgtTimezone) %>% | |
with_tz(tz="UTC"), | |
utcLocalMidnightOffset = utcLocalMidnight %>% | |
hour() | |
) %>% | |
filter((utcLocalMidnightOffset != lag(utcLocalMidnightOffset)) | (row_number() == 1)) %>% | |
mutate(tz=tgtTimezone) %>% | |
select(tz, everything()) %>% | |
select(-utcLocalMidnightOffset) | |
} | |
getMidnightDSTUTC("America/Chicago", 2021) | |
getMidnightDSTUTC("America/Sao_Paulo", 2021) | |
dsts_df <- | |
c( "America/New_York", | |
"America/Chicago", | |
"America/Los_Angeles", | |
"America/Denver", | |
"America/Indiana/Indianapolis", | |
"America/Detroit", | |
"America/Phoenix", | |
"America/Kentucky/Louisville", | |
"America/Toronto", | |
"America/Vancouver", | |
"America/Monterrey", | |
"Pacific/Honolulu", | |
"America/Indiana/Petersburg", | |
"America/Indiana/Marengo", | |
"America/Sao_Paulo", | |
"America/Puerto_Rico", | |
"America/Mexico_City", | |
"America/Kentucky/Monticello", | |
"America/Indiana/Vincennes", | |
"America/Boise", | |
"Canada/Eastern", | |
"Asia/Singapore", | |
"Asia/Calcutta", | |
"America/Tijuana", | |
"America/Panama", | |
"America/Edmonton", | |
"America/Anchorage") %>% | |
map_dfr(~{ | |
getMidnightDSTUTC(.x, 2021) | |
}) | |
View(dsts_df) | |
#;; List local midnight start dates for all Olson Timezones | |
dsts_df <- | |
OlsonNames() %>% | |
map_dfr(~{ | |
getMidnightDSTUTC(.x, 2021) | |
}) | |
dsts_df %>% | |
select(tz, utcLocalMidnight) %>% | |
arrange(tz, utcLocalMidnight) %>% | |
group_by(tz) %>% | |
mutate(elt = row_number()) %>% | |
pivot_wider(names_from = "elt", values_from = "utcLocalMidnight") %>% | |
ungroup() %>% | |
set_names(c("tz", "jan", "first", "second")) #%>% write_csv(here::here("dat", "tz-change-listing.csv")) |
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