R help - Sep 2013 - POSIXlt and months

The help page for as.POSIXlt suggests using it as a way to extract month, day,
and year.
However, I can't find any documentation on the results and am a bit
surprised by the month
portion.

An example, run about 6:21 AM on Sept 3.

 > unlist(unclass(as.POSIXlt(Sys.time())))

       sec       min      hour      mday       mon      year      wday      yday
  43.24545  21.00000   6.00000   3.00000   8.00000 113.00000   2.00000 245.00000
     isdst
   1.00000


So: it appears that I need to
       add 1900 to year
       add 1 to month
but other components are as I would expect.

 > unlist(unclass(as.POSIXlt(as.Date("1953/03/10"))))
   sec   min  hour  mday   mon  year  wday  yday isdst
     0     0     0    10     2    53     2    68     0

Supports a 0 origin for everything except year and mday.

  A pointer to formal documentation of this would make me feel easier about
using the
function.

Terry Therneau

On Tue, Sep 3, 2013 at 7:31 AM, Terry Therneau <therneau at mayo.edu>
wrote:
> The help page for as.POSIXlt suggests using it as a way to extract month,
> day, and year.
> However, I can't find any documentation on the results and am a bit
> surprised by the month portion.
>
> An example, run about 6:21 AM on Sept 3.
>
>> unlist(unclass(as.POSIXlt(Sys.time())))
>
>       sec       min      hour      mday       mon      year      wday
> yday
>  43.24545  21.00000   6.00000   3.00000   8.00000 113.00000   2.00000
> 245.00000
>     isdst
>   1.00000
>
>
> So: it appears that I need to
>       add 1900 to year
>       add 1 to month
> but other components are as I would expect.
>
>> unlist(unclass(as.POSIXlt(as.Date("1953/03/10"))))
>   sec   min  hour  mday   mon  year  wday  yday isdst
>     0     0     0    10     2    53     2    68     0
>
> Supports a 0 origin for everything except year and mday.
>
>  A pointer to formal documentation of this would make me feel easier about
> using the function.
?DateTimeClasses


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