Negative years with strptime?

Is there a way to make as.Date() and strptime() process strings with
negative years? It appears that Date objects can contain negative years and
you can convert them to strings, but you can't convert them back to Date
objects.


x <- as.Date(c("0001-01-24", "0500-01-24"))
as.character(x)
# "0001-01-24" "0500-02-02"
as.Date(as.character(x))
# "0001-01-24" "0500-01-24"

# Minus 391 days gives negative year
as.character(x - 391)
# "-001-12-30" "0498-12-29"

# Can't convert this string back to Date
as.Date(as.character(x - 391))
# Error during wrapup: character string is not in a standard unambiguous
format


# as.Date.character uses strptime, so we can try using strptime directly
strptime(as.character(x), "%Y-%m-%d")
# "0001-01-24" "0500-01-24"

strptime(as.character(x - 391), "%Y-%m-%d")
# NA           "0498-12-29"


Thanks,
-Winston

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Hello,

Is there a bug with negative dates? Just see:

seq(as.Date("0000-01-01"), length = 22, by = "-1 year")
 [1] "0000-01-01" "000/-01-01" "000.-01-01" "000--01-01" "000,-01-01"
 [6] "000+-01-01" "000*-01-01" "000)-01-01" "000(-01-01" "000'-01-01"
[11] "00/0-01-01" "00//-01-01" "00/.-01-01" "00/--01-01" "00/,-01-01"
[16] "00/+-01-01" "00/*-01-01" "00/)-01-01" "00/(-01-01" "00/'-01-01"
[21] "00.0-01-01" "00./-01-01"

See the year number: "after" the zero, i.e., downward from zero, the printed
character is '/' which happens to be the ascii character before '0', and
before it's '.', etc. This sequence gives the nine ascii characters before
zero as last digit of the year, then the 10th is '0' as (now) expected, then
goes to the second digit, etc.

It seems to stop at the first 9, or else we would have some sort of real
problem.

Anyway, this doesn't look right.

Rui Barradas
Em 10-07-2012 22:17, Winston Chang escreveu:

Is there a way to make as.Date() and strptime() process strings with
negative years? It appears that Date objects can contain negative years
and
you can convert them to strings, but you can't convert them back to Date
objects.


x <- as.Date(c("0001-01-24", "0500-01-24"))
as.character(x)
# "0001-01-24" "0500-02-02"
as.Date(as.character(x))
# "0001-01-24" "0500-01-24"

# Minus 391 days gives negative year
as.character(x - 391)
# "-001-12-30" "0498-12-29"

# Can't convert this string back to Date
as.Date(as.character(x - 391))
# Error during wrapup: character string is not in a standard unambiguous
format


# as.Date.character uses strptime, so we can try using strptime directly
strptime(as.character(x), "%Y-%m-%d")
# "0001-01-24" "0500-01-24"

strptime(as.character(x - 391), "%Y-%m-%d")
# NA           "0498-12-29"


Thanks,
-Winston

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It looks different on my system (Mac, R 2.15.1)

seq(as.Date("0000-01-01"), length = 22, by = "-1 year")
  [1] "0000-01-01" "-001-01-01" "-002-01-01" "-003-01-01" "-004-01-01"
  [6] "-005-01-01" "-006-01-01" "-007-01-01" "-008-01-01" "-009-01-01"
[11] "-010-01-01" "-011-01-01" "-012-01-01" "-013-01-01" "-014-01-01"
[16] "-015-01-01" "-016-01-01" "-017-01-01" "-018-01-01" "-019-01-01"
[21] "-020-01-01" "-021-01-01"

So in addition to the issues with converting a negative-year string to a
Date, it looks like converting a negative date to a string with
as.character.Date() is probably also not consistent.

It certainly would be useful to have a way of handling dates with
negative years.

-Winston


On Tue, Jul 10, 2012 at 4:59 PM, Rui Barradas <ruipbarradas at sapo.pt
<mailto:ruipbarradas at sapo.pt>> wrote:

    Hello,

    Is there a bug with negative dates? Just see:

    seq(as.Date("0000-01-01"), length = 22, by = "-1 year")
      [1] "0000-01-01" "000/-01-01" "000.-01-01" "000--01-01" "000,-01-01"
      [6] "000+-01-01" "000*-01-01" "000)-01-01" "000(-01-01" "000'-01-01"
    [11] "00/0-01-01" "00//-01-01" "00/.-01-01" "00/--01-01" "00/,-01-01"
    [16] "00/+-01-01" "00/*-01-01" "00/)-01-01" "00/(-01-01" "00/'-01-01"
    [21] "00.0-01-01" "00./-01-01"

    See the year number: "after" the zero, i.e., downward from zero, the
    printed character is '/' which happens to be the ascii character
    before '0', and before it's '.', etc. This sequence gives the nine
    ascii characters before zero as last digit of the year, then the
    10th is '0' as (now) expected, then goes to the second digit, etc.

    It seems to stop at the first 9, or else we would have some sort of
    real problem.

    Anyway, this doesn't look right.

    Rui Barradas
    Em 10-07-2012 22:17, Winston Chang escreveu:

        Is there a way to make as.Date() and strptime() process strings with
        negative years? It appears that Date objects can contain
        negative years and
        you can convert them to strings, but you can't convert them back
        to Date
        objects.


        x <- as.Date(c("0001-01-24", "0500-01-24"))
        as.character(x)
        # "0001-01-24" "0500-02-02"
        as.Date(as.character(x))
        # "0001-01-24" "0500-01-24"

        # Minus 391 days gives negative year
        as.character(x - 391)
        # "-001-12-30" "0498-12-29"

        # Can't convert this string back to Date
        as.Date(as.character(x - 391))
        # Error during wrapup: character string is not in a standard
        unambiguous
        format


        # as.Date.character uses strptime, so we can try using strptime
        directly
        strptime(as.character(x), "%Y-%m-%d")
        # "0001-01-24" "0500-01-24"

        strptime(as.character(x - 391), "%Y-%m-%d")
        # NA           "0498-12-29"


        Thanks,
        -Winston

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