R notebook dates, making dates to decades

I don't know of any package or function that facilitates "decades", though since we're working with integer years, it should be relatively straight-forward. Here are two base R methods with about the same performance.

set.seed(42)
dates <- as.Date("2000-01-01") + sample(10000, size = 5)
dates
# [1] "2006-06-27" "2014-06-09" "2025-06-08" "2003-06-06" "2024-03-01"

10 * (as.integer(format(dates, format = "%Y")) %/% 10)
# [1] 2000 2010 2020 2000 2020

10 * floor(as.integer(format(dates, format = "%Y")) / 10)
# [1] 2000 2010 2020 2000 2020

Edit: much faster method, in case performance is an issue:

10 * ((as.POSIXlt(dates)$year + 1900) %/% 10)

I believe this is faster because it does not convert to and from strings, so numeric ops are a bit faster. The POSIXlt (as opposed to POSIXct) storage of a timestamp bases the year on 1900:

Sys.Date()
# [1] "2022-01-17"
dput(as.POSIXlt(Sys.Date()))
# structure(list(sec = 0, min = 0L, hour = 0L, mday = 17L, mon = 0L, 
#     year = 122L, wday = 1L, yday = 16L, isdst = 0L), class = c("POSIXlt", 
# "POSIXt"), tzone = "UTC")

which is fairly easy to work around.

Benchmark:

bench::mark(
  intdiv  = 10 * (as.integer(format(dates, format = "%Y")) %/% 10), 
  floor   = 10 * floor(as.integer(format(dates, format = "%Y")) / 10), 
  posixlt = 10 * ((as.POSIXlt(dates)$year + 1900) %/% 10)
)
# # A tibble: 3 x 13
#   expression      min   median `itr/sec` mem_alloc `gc/sec` n_itr  n_gc total_time result         memory              time             gc                
#   <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl> <int> <dbl>   <bch:tm> <list>         <list>              <list>           <list>            
# 1 intdiv       16.2ms   19.9ms      48.1     978KB     2.00    24     1      499ms <dbl [10,000]> <Rprofmem [21 x 3]> <bench_tm [25]>  <tibble [25 x 3]> 
# 2 floor        16.2ms   21.5ms      48.0     978KB     2.09    23     1      480ms <dbl [10,000]> <Rprofmem [21 x 3]> <bench_tm [24]>  <tibble [24 x 3]> 
# 3 posixlt     740.2us  796.2us     941.      469KB    15.4    427     7      454ms <dbl [10,000]> <Rprofmem [10 x 3]> <bench_tm [434]> <tibble [434 x 3]>