dates ← {g←¯53799} ##.date daynos ⍝ ⎕TS format from day number.
The argument is an array of day numbers since 1899-12-31 00:00:00. The resulting
array has rank one greater than [daynos] where 7-vectors along the new last axis
are ⎕TS-style date and time: (↓date ⍵)≡date¨⍵.
Optional left argument {g} specifies the day number of the →Gregorian_calendar←
reform (default ¯53799 ←→ 1752-09-02). This is of interest only when exploring
historical dates.
(
Bug: Although [date] accounts for the "removal" of 11 days in September 1752
for the change to the Gregorian calendar, it does not accommodate the att-
endant change to New Year's Day. Prior to the implementation of the
→British_Calendar_Act_1751← the year changed at midnight on the 24th March,
making 25th March New Year's Day. The following pairs of dates should be
contiguous in the British calendar:
1750-03-24 1751-03-25 ⍝ Julian year change in March 1750.
1751-12-31 1752-01-01 * ⍝ Calendar Act year change on Dec 31 in 1751.
1752-03-24 1752-03-25 ⍝ no Julian year change March 1752.
1752-09-02 1752-09-14 ⍝ change to Gregorian calendar.
1752-12-31 1753-01-01 ⍝ normal Gregorian year change 1752-1753.
* "... according to which the Year of our Lord beginneth on the 25th Day of
March, shall not be made use of from and after the last Day of December
1751; and that the first Day of January next following the said last Day of
December shall be reckoned, taken, deemed and accounted to be the first Day
of the Year of our Lord 1752; ..."
)
Ref: Jean Meeus, "Astronomical Algorithms", p59. ISBN 0-943396-61-1, 1998.
Peter-Michael Hager suggests this nifty one-liner, which is good for dates be-
tween 1752-09-14 and 2400-02-28:
n_date←{y,m,1+d-(m←m+.≤d)⊃m←+\0 31,(29-×4|1⊃y d←⌊0 365.25⊤694035+⌊(36525×⍵-60.5+0.5××⍵-36584)÷36524),9⍴5⍴31 30}
Examples:
date 12791 ⍝ Whole number of days.
1935 1 8 0 0 0 0
date 12791.51388889 ⍝ Part way through day.
1935 1 8 12 20 0 0
show←timestamp∘'' ⍝ Format ⎕TS vector.
show date 1e5÷3 ⍝ Fractional number of days.
1991-04-06 08:00:00
show date ¯7596.520833 ⍝ Negative days before 1899 12 31.
1879-03-14 11:30:00
date 2 2⍴14892 15509 15761 14798 ⍝ (⍴date ⍵) ≡ (⍴⍵),7.
1940 10 9 0 0 0 0
1942 6 18 0 0 0 0
1943 2 25 0 0 0 0
1940 7 7 0 0 0 0
date ¯53799 + 0 1 ⍝ 1752 calendar reform
1752 9 2 0 0 0 0
1752 9 14 0 0 0 0
⎕ts≡date days ⎕ts ⍝ Full circle.
1
eudate←¯115860∘date ⍝ European calendar reform:
eudate ¯115860+0 1 ⍝ 1582: Oct 4th and 15th contiguous.
1582 10 4 0 0 0 0
1582 10 15 0 0 0 0
See also: Dates days cal timestamp
See also: Gregorian_calendar British_Calendar_Act_1751
Back to: contents
Back to: Workspaces