Compute Time Gain/Loss due to Daylight Saving Time

DST2GL computes, for each date-time entry, how many hours a day deviates from the standard 24hours because of DST shifts. Internally it calls Date2TotalT() in seconds, subtracts the 86400s of a normal day, and converts the remainder to hours.

Usage

DST2GL(DT, TZ = "local")

Arguments

DT

A vector of class Date, POSIXct, or POSIXlt, sorted in ascending order. Each element marks the start of a day boundary. To capture DST transitions, include at least one day before and after the expected shift. Note that the time zone should be specified in the DT. See as.POSIXct.

TZ

The time zone when the recording started. (default = "local", which means user's local time zone)

Value

A numeric vector of the same length as DT. Each value is the number of hours that day is longer (positive) or shorter (negative) than 24h. A zero means no DST shift on that date.

Examples

# Example around a typical spring-forward transition (e.g. US second Sunday
# in March)
dates <- as.Date ("2021-03-14")

# On 2021-03-14 clocks jumped forward: day is 23h so output = -1
DST2GL (dates)
#> 2021-03-14 
#>         -1 


# Example around a fall-back transition (e.g. first Sunday in November)
dates <- as.Date ("2021-11-07")

# On 2021-11-07 clocks fall back: day is 25h so output = +1
DST2GL (dates)
#> 2021-11-07 
#>          1 

# Multiple Dates
sapply (c ("2021-03-13", "2021-03-14", "2021-03-15"), DST2GL)
#> 2021-03-13.2021-03-13 2021-03-14.2021-03-14 2021-03-15.2021-03-15 
#>                     0                    -1                     0