Skip to contents

Daylight Saving Time

Source: R/DST.R
DST.Rd

Determine if Dates Fall in Daylight Saving Time for the Given Time Zone(s)

Usage

DST(DT, TZ = "local")

Arguments

DT

A vector of class `Date`, `POSIXct`, or `POSIXlt`, representing the dates/times to test. These need not be sorted.

TZ

A single string naming an IANA time zone (e.g. `America/New_York`). If `"local"`, it will extract local time zone using Sys.timezone. Must match one entry in OlsonNames.

Value

A logical vector of the same length as `DT`.

  • `TRUE` indicates the timestamp falls in DST

  • `FALSE` indicates standard time.

Details

For each element of `DT`, returns `TRUE` if that date-time is in daylight saving time (DST) under the specified time zone. The function handles transitions by detecting the "gain" or "loss" of hours via `DST2GL()` and flipping the DST flag on the transition day.

Examples

# Standard use: New York in summer vs. winter
dates <- as.POSIXct (c ("2021-06-15", "2021-12-15"), tz = "America/New_York")
DST (dates, TZ = "America/New_York")
#> 2021-06-15 2021-12-15 
#>       TRUE      FALSE 


# Around the spring-forward transition
trans <- as.Date (c ("2021-03-13", "2021-03-14", "2021-03-15"))
DST (trans, TZ = "America/New_York")
#> 2021-03-13 2021-03-14 2021-03-15 
#>      FALSE       TRUE      FALSE 

# Using the local system time zone
DST (as.POSIXct ("2023-07-01 12:00:00"), TZ = "local")
#> 2023-07-01 12:00:00 
#>                TRUE