SAS creating a season variable from a date variable [closed] - date

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I am trying to create a season variable from a date variable so if the date is 09/09/2010 then the season would be "Fall".
Can anyone help?
Thanks

Answer 1

Assuming this is based on the month/day calculation. It depends on the exact logic, but something like this would work.
Use MONTH() to calculate the month of the year and then use that to assign the season. If you need to account for specific days, ie Winter is Dec 22 to Mar 22 then you can also use the DAY() function to get the day of the month.
data want;
set sashelp.stocks (where = stocks='IBM');
length Season $10.;
if month(date) in (3, 4, 5) then season = 'Spring';
else if month(date) in (6, 7, 8) then season = 'Fall';
else if ....;
else if ....;
else season = 'CHECK ME';
run;
Almost all SAS installations ship with the SASHELP library so you should be able to run this automatically.

Answer 2

You probably want to create a custom format based on a table of season start dates downloaded from the interwebs.
Or you could use a web api such as https://www.timeanddate.com/services/api/holiday-api.html
Or if you are a computational masochist, deal with the computed equinox based on lat and long.
From "https://aa.usno.navy.mil/faq/docs/GAST.php" (the page has a security certificate error)
Sidereal time is a system of timekeeping based on the rotation of
the Earth with respect to the fixed stars in the sky. More
specifically, it is the measure of the hour angle of the vernal
equinox. If the hour angle is measured with respect to the true
equinox, apparent sidereal time is being
measured. If the hour angle is measured with respect to the mean
equinox, mean sidereal time is being
measured. When the measurements are made with respect to the meridian
at Greenwich, the times are referred to as Greenwich mean sidereal
time (GMST) and Greenwich apparent sidereal time (GAST).
Given below is a simple algorithm for computing apparent sidereal
time to an accuracy of about 0.1 second, equivalent to about
1.5 arcseconds on the sky. The input time required by the algorithm is represented as a Julian date (
Julian dates can be used to determine
Universal Time.)
Let JD be the Julian date of the time of interest. Let
JD0 be the Julian date of the previous
midnight (0h) UT (the value of
JD0 will end in .5 exactly), and let H
be the hours of UT elapsed since that time. Thus we have
JD = JD0 + H/24.
For both of these Julian dates, compute the number of days and
fraction (+ or -) from 2000 January 1, 12h UT, Julian date 2451545.0:
D = JD - 2451545.0
D0 = JD0 - 2451545.0
Then the Greenwich mean sidereal time in hours is
GMST = 6.697374558 + 0.06570982441908 D0 + 1.00273790935 H + 0.000026 T2
where T = D/36525 is the number of centuries since the year 2000;
thus the last term can be omitted in most applications. It will be
necessary to reduce GMST to the range 0h to 24h.
Setting H = 0 in the above formula yields the Greenwich mean sidereal
time at 0h UT, which is tabulated in
The Astronomical Almanac.
The following alternative formula can be used with a loss of
precision of 0.1 second per century:
GMST = 18.697374558 + 24.06570982441908 D
where,
as above, GMST must be reduced to the range 0h to 24h.
The equations for GMST given above are adapted from those given in
Appendix A of USNO
Circular No. 163 (1981).
The Greenwich apparent sidereal time is obtained by adding a
correction to the Greenwich mean sidereal time computed above. The
correction term is called the nutation in right ascension or
the equation of the equinoxes. Thus,
GAST = GMST + eqeq.
The equation of the equinoxes
is given as eqeq = Δψ cos ε where Δψ, the nutation in longitude, is given
in hours approximately by
Δψ ≈ -0.000319 sin Ω - 0.000024 sin 2L
with Ω, the Longitude of the ascending node of the Moon, given as
Ω = 125.04 - 0.052954 D,
and L,
the Mean Longitude of the Sun, given as
L = 280.47 + 0.98565 D.
ε is the obliquity and is given as
ε = 23.4393 - 0.0000004 D.
The above expressions for Ω, L, and ε are all expressed
in degrees.
The mean or apparent sidereal time locally is found by
obtaining the local longitude in degrees, converting it to hours by
dividing by 15, and then adding it to or subtracting it from the
Greenwich time depending on whether the local position is east (add)
or west (subtract) of Greenwich.
If you need apparent sidereal time to better than 0.1 second
accuracy on a regular basis, consider using the Multiyear Interactive
Computer Almanac,
MICA.
MICA
provides very accurate almanac data in tabular form for a range of
years.
NOTES ON ACCURACY
The maximum error resulting from the use of the above formulas for
sidereal time over the period 2000-2100 is 0.432 seconds; the RMS
error is 0.01512 seconds. To obtain sub-second accuracy in
sidereal time, it is important to use the form of Universal Time
called UT1 as the basis for the input
Julian date.
The maximum value of the equation of the equinoxes is about 1.1
seconds, so if an error of ~1 second is unimportant, the last
series of formulas can be skipped entirely. In this case set
eqeq = 0 and GAST = GMST, and use either UT1 or UTC as the Universal Time basis for the
input Julian date.