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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