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Russell [EMAIL PROTECTED]
The simple way, in REBOL, to convert the day-of-week integers, 0 to 6, to
the corresponding strings, Sunday, Monday, etc is to create the block
dowdb: [0 "Sunday" 1 "Monday" 2 "Tuesday" 3 "Wednesday" 4 "Thursday" 5
"Friday" 6 "Saturday"]
then select dowdb 1 returns "Monday", etc.
You can omit the "", then the entries are simply words and the select
function will return the words.
select dowdb 7 returns none
dowdb is a simple data-base.
Some time ago some of us were messing around with Julian Day numbers, which
are easily converted to DOW numbers by the mod 7 operation. A script
julian.r is attached. It defines a number of functions to convert dates to
Julian day numbers, etc.
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REBOL
[ Title: {Julian Calendar Stuff}
date: 8-11-1999
file: %julian.r
author: {Russ Yost}
Email: [EMAIL PROTECTED]
Purpose: { To provide conversions to/from julian day numbers/dates }
Category: 'utility
Comment: {I'm not sure where these algorithms originated, but I used
them in a JForth program in 1992. The epoch date seems to be
that set by Joseph Scaliger in 1582, i.e., Jan 1 4713 BC, (that
would be Julian day number 1), but as this algorithm takes the
average length of the solar year as 365.2425, it works over the
range 0001 through 3000. Beyond then, the discrepancy with the
true length, 365.242199, should lead to errors.
(The year 2000, being divisible by 400, will be a leap year,
although in general, years that are multiples of 100 are not
leap years. It *does* yield the correct Julian Day number given
in the 1999 World Almanac (World Almanac Books, Mahwah NJ) pg
322, for 31 Dec 1998, 2,451,179.)
}
]
print {
Two functions are defined herein, date-to-jul, with argument a
date in format dd-mm-yyyy in year range 0001 through 3000, and
jul-to-date, with argument a julian day number (JD) based on 1 Jan
4713 BC, with 31 Dec 1998's JD = 2451179 (as given in the 1999
Almanac) and corresponding to the above mentioned range.
This latter function also provides the day of the week for
the given JD.
Some other useful functions:
diy, arg yyyy, yields the number of days in a given year.
febdays, arg yyyy, yields the number of days in February.
testj-d, arg yyyy, prints a yyyy calendar, 1 line per month.
}
jul0: 1720997 ; use with jul day based in 365.2425 days in year.
comment {There are 365.242199 solar days in a year, so the preceding
assumption will lead to trouble after year 3000, I think.}
comment { 'jul0 also compensates for extra days added in the calculation
of the number of days per month, and adjusts the result to agree
with 1999 Almanac's statement that JD of 31 Dec 1998 is
2,451,179.
}
daysinyear: 365.2425
daysinmo: 30.6001 ; a synthesized number that is used to calc
; days in each month.
weekdays: ["Sun" "Mon" "Tue" "Wed" "Thu" "Fri" "Sat"]
idiv: func [x y][to-integer ( divide x y) ]
comment {REBOL ought to include an integer divide function! }
comment { Th func 'dye calcs a Julian day no based on 1-1-0001, taking
into account years that are multiples of 4 are leap years
(Feb has 29 days instead of 28) unless they're multiples of
100 years, but those *are* leap years if they're multiples of
400.
}
comment {dye is day number of last day of year y }
dye: func[y][ (y * 365) + (((idiv y 4) - (idiv y 100)) + (idiv y 400))]
date-to-jul: func [date /local jul mo mox yr][
jul: date/day + jul0
yr: date/year
mo: date/month
either mo > 2 [mox: mo + 1 ] [
mox: mo + 13 yr: yr - 1 ]
jul: jul + (dye yr) + (to-integer mox * daysinmo)
]
jul-to-date: func [jl /local date da mo yr dano][
dano: jl - jul0
dow: remainder (dano + 6) 7 ; Sunday = 0
date: j2d jl
da: date/day mo: date/month yr: date/year
print [{date is } to-date reduce[da mo yr]]
print [{ day of week is }first skip weekdays dow]
]
j2d: func [ jl /local dano yr mo da dow mox][
dano: jl - jul0
yr: to-integer ((dano - 122.1) / daysinyear) ; print yr
mox: to-integer((dano - (to-integer(yr * daysinyear))) / daysinmo)
da: dano - (to-integer(yr * daysinyear))
da: da - (to-integer (mox * daysinmo))
either mox < 14 [mo: mox - 1][ mo: mox - 13]
if mo < 3 [yr: yr + 1]
return to-date reduce [da mo yr]
]
comment { jdye is JD of last day of year }
jdye: func [y][ date-to-jul (to-date reduce [31 12 y])]
comment {'diy yields the number of days in a year - useful for checking
leap years. }
diy: func [y][(jdye y )- (jdye (y - 1))]
febdays: func[y]
[(date-to-jul (to-date reduce[1 3 y])) - date-to-jul (to-date
reduce[1 2 y])]
comment {'testj-d prints a calendar, 1 line per month for its argument,
a year in format yyyy }
testj-d: func[yr /local strt-dt stjul dx da][
strt-dt: to-date reduce [1 1 yr]
stjul: date-to-jul strt-dt
print {}
for i 1 diy yr 1 [
dx: j2d ( stjul + (i - 1))
da: dx/day
either da = 1 [
prin [{^(line)} da {}]][
prin [da {}]]
]
print ""
]
