How to properly convert, achieve the equivalence of dates

General
1

How to properly convert, achieve the equivalence of dates
How to achieve the expected value with the functions to manipulate dates, used in each data.table.
In the case of as.Date, I have varied the origin without achieving the expected result
What to do?
On many occasions I find this numerical format of dates!
the 20200402 format is used on this site

library(data.table)
dt<-as.data.table(list(
                       yr = c(14610, 14975, 15340, 15706, 16071, 16436, 16801, 17167, 
                              17532, 17897, 18262, 18628, 18993, 19358, 19723, 20089,
                              20454, 20819, 21184, 21550, 21915, 22280, 22645, 23011, 
                              23376, 23741, 24106, 24472, 24837, 25202, 25567, 25933, 
                              26298, 26663, 27028, 27394, 27759,  28124, 28489, 28855)))
#help as.Date {base}
## date given as number of days since 1900-01-01 (a date in 1989)
#as.Date(32768, origin = "1900-01-01")
dt[,`:=`(expected=as.IDate(yr),date=as.Date(yr,origin = "1900-01-01")),]
print(dt,topn=3)
      yr   expected       date
 1: 14610 2010-01-01 1940-01-02
 2: 14975 2011-01-01 1941-01-01
 3: 15340 2012-01-01 1942-01-01
---                            
38: 28124 2047-01-01 1977-01-01
39: 28489 2048-01-01 1978-01-01
40: 28855 2049-01-01 1979-01-02

dt2<-as.data.table(list(
  yr = c(20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,
         20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,
         20200327,20200327,20200327)))
dt2[,`:=`(expected=lubridate::ymd(yr),idate=as.IDate(yr),date=as.Date(yr,origin = "1900-01-01")),]
print(dt2,topn=3)
         yr   expected       idate        date
 1: 20200327 2020-03-27 57276-08-13 57206-08-14
 2: 20200327 2020-03-27 57276-08-13 57206-08-14
 3: 20200327 2020-03-27 57276-08-13 57206-08-14
---                                            
19: 20200327 2020-03-27 57276-08-13 57206-08-14
20: 20200327 2020-03-27 57276-08-13 57206-08-14
21: 20200327 2020-03-27 57276-08-13 57206-08-14
2

Try 1970
Or use lubridate? You second example shows you had success using lubridate already.

3

Do these work for you?

library(data.table)
dt<-as.data.table(list(
  yr = c(14610, 14975, 15340, 15706, 16071, 16436, 16801, 17167, 
         17532, 17897, 18262, 18628, 18993, 19358, 19723, 20089,
         20454, 20819, 21184, 21550, 21915, 22280, 22645, 23011, 
         23376, 23741, 24106, 24472, 24837, 25202, 25567, 25933, 
         26298, 26663, 27028, 27394, 27759,  28124, 28489, 28855)))
dt[,`:=`(expected=as.IDate(yr),date=as.Date(yr,origin = "1970-01-01")),]
print(dt,topn=3)
#>        yr   expected       date
#>  1: 14610 2010-01-01 2010-01-01
#>  2: 14975 2011-01-01 2011-01-01
#>  3: 15340 2012-01-01 2012-01-01
#> ---                            
#> 38: 28124 2047-01-01 2047-01-01
#> 39: 28489 2048-01-01 2048-01-01
#> 40: 28855 2049-01-01 2049-01-01

dt2<-as.data.table(list(
  yr = c(20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,
         20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,20200327,
         20200327,20200327,20200327)))
dt2[,`:=`(expected=lubridate::ymd(yr),idate=as.IDate(as.character(yr),format="%Y%m%d"),
          date=as.Date(as.character(yr),format="%Y%m%d")),]
print(dt2,topn=3)
#>           yr   expected      idate       date
#>  1: 20200327 2020-03-27 2020-03-27 2020-03-27
#>  2: 20200327 2020-03-27 2020-03-27 2020-03-27
#>  3: 20200327 2020-03-27 2020-03-27 2020-03-27
#> ---                                          
#> 19: 20200327 2020-03-27 2020-03-27 2020-03-27
#> 20: 20200327 2020-03-27 2020-03-27 2020-03-27
#> 21: 20200327 2020-03-27 2020-03-27 2020-03-27

Created on 2020-04-03 by the reprex package (v0.3.0)

4

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