[Rd] R doesn't understand dates prior to 1 Jan 1970

[William Faulk]

I'm installing R on an Irix 6.5 machine and R fails to understand dates 
prior to 1 Jan 1970.  This first cropped up early in the test scripts 
(Examples/base-Ex.R):

> > seq(as.Date("1910/1/1"), as.Date("1999/1/1"), "years")
> Error in fromchar(x) : character string is not in a standard unambiguous format

The root there is the as.Date("1910/1/1"), which returns that same error 
when entered alone.  Any date on or after 1 Jan 1970 works fine; any 
before fails with the same error.  Obviously, I've not tried every date, 
but that seems to be the case.

I got by that test by changing "1910" to "1970", but it crops up later, 
too (reg-tests-1.R):

> > ## Date objects with NA's
> > (t1 <- strptime(c("6. Aug. 1930", "3. Nov. 1925", "28. Mar. 1959",
> +                  NA, paste(1:29," Feb. 1960", sep=".")),
> +                format = "%d. %b. %Y"))
>  [1] "1930-08-06" "1925-11-03" "1959-03-28" NA           "1960-02-01"
>  [6] "1960-02-02" "1960-02-03" "1960-02-04" "1960-02-05" "1960-02-06"
> [11] "1960-02-07" "1960-02-08" "1960-02-09" "1960-02-10" "1960-02-11"
> [16] "1960-02-12" "1960-02-13" "1960-02-14" "1960-02-15" "1960-02-16"
> [21] "1960-02-17" "1960-02-18" "1960-02-19" "1960-02-20" "1960-02-21"
> [26] "1960-02-22" "1960-02-23" "1960-02-24" "1960-02-25" "1960-02-26"
> [31] "1960-02-27" "1960-02-28" "1960-02-29"
> > stopifnot(6 == length(print(s1 <- summary(t1))),
> +           s1== summary(as.POSIXct(t1)),
> +           6 == length(print(format(as.Date(s1)))) )
>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
>      NA      NA      NA      NA      NA      NA
>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
>      NA      NA      NA      NA      NA      NA
> Error in if (!(is.logical(r <- eval(ll[[i]])) && all(r))) stop(paste(deparse(mc[
> [i +  :
>         missing value where TRUE/FALSE needed
> Execution halted

Interestingly, strptime() seems to return the correct results, as can be 
seen in the output above, but the problem occurs in summary() and in 
as.POSIXct():

> > summary(t1)
>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
>      NA      NA      NA      NA      NA      NA 
> > as.POSIXct(t1)
>  [1] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
> [26] NA NA NA NA NA NA NA NA

This check, too, can be avoided if I change the dates created:

> > (t1 <- strptime(c("6. Aug. 1970", "3. Nov. 19725", "28. Mar. 1979",
> + NA, paste(1:29," Feb. 1980", sep=".")),
> + format = "%d. %b. %Y"))
>  [1] "1970-08-06" "1972-11-03" "1979-03-28" NA           "1980-02-01"
>  [6] "1980-02-02" "1980-02-03" "1980-02-04" "1980-02-05" "1980-02-06"
> [11] "1980-02-07" "1980-02-08" "1980-02-09" "1980-02-10" "1980-02-11"
> [16] "1980-02-12" "1980-02-13" "1980-02-14" "1980-02-15" "1980-02-16"
> [21] "1980-02-17" "1980-02-18" "1980-02-19" "1980-02-20" "1980-02-21"
> [26] "1980-02-22" "1980-02-23" "1980-02-24" "1980-02-25" "1980-02-26"
> [31] "1980-02-27" "1980-02-28" "1980-02-29"
> > summary(t1)
>                      Min.                   1st Qu.                    Median 
> "1970-08-06 00:00:00 EDT" "1980-02-05 18:00:00 EST" "1980-02-13 12:00:00 EST" 
>                      Mean                   3rd Qu.                      Max. 
> "1979-07-28 00:58:07 EDT" "1980-02-21 06:00:00 EST" "1980-02-29 00:00:00 EST" 
> > as.POSIXct(t1)
>  [1] "1970-08-06 EDT" "1972-11-03 EST" "1979-03-28 EST" NA              
>  [5] "1980-02-01 EST" "1980-02-02 EST" "1980-02-03 EST" "1980-02-04 EST"
>  [9] "1980-02-05 EST" "1980-02-06 EST" "1980-02-07 EST" "1980-02-08 EST"
> [13] "1980-02-09 EST" "1980-02-10 EST" "1980-02-11 EST" "1980-02-12 EST"
> [17] "1980-02-13 EST" "1980-02-14 EST" "1980-02-15 EST" "1980-02-16 EST"
> [21] "1980-02-17 EST" "1980-02-18 EST" "1980-02-19 EST" "1980-02-20 EST"
> [25] "1980-02-21 EST" "1980-02-22 EST" "1980-02-23 EST" "1980-02-24 EST"
> [29] "1980-02-25 EST" "1980-02-26 EST" "1980-02-27 EST" "1980-02-28 EST"
> [33] "1980-02-29 EST"

Anyone have any ideas?

-Bitt