iCalendar recurrence rule for event that occurs every two years in multiple months on first weekend day

Question

Is it possible to specify an event to occur on the 1st weekend day of multiple months every 2 years in a single RRULE? Using February and September as a test case, my first thought was:

FREQ=YEARLY;DTSTART=20140320T070000Z;INTERVAL=2;BYSETPOS=1;BYMONTH=2,9;BYDAY=SA,SU

but BYSETPOS reduces the set down to February only. I thought changing the freq to monthly would do the trick after I posted here, but applying an interval of 2 for every other year messes things up because the interval is applied to a monthly freq instead of a yearly freq.

I made this a new question because I did not include interval in my original question.

I think splitting this into multiple rrules would work, but it would greatly increase the complexity of this area of my app so I was hoping for a single rrule with a yearly freq.

Thanks!

Answer 1

FWIW, and since you mention it as a potential workaround, RFC5545 has removed the ability to have multiple RRULE property in a single VEVENT/VTODO (https://www.rfc-editor.org/rfc/rfc5545#section-3.6.1). It was there in RFC2445.

Then, unless someone finds a very elegant and simple solution, you may be left with something that is so convoluted that most clients will barf on it (don't know how interoperability is important to you).

This leaves you with 2 choices I think:

• either use 2 different events (maybe linked with a RELATED-TO property)
• or, if you can bound the event to a certain number of instances, represent it as a set of RDATE (or RRULE + RDATE, or RRULE + EXDATE, etc...).

Answer 2

Adding BYSETPOS like this may work as you intend:

FREQ=YEARLY;INTERVAL=2;BYMONTH=2,9;BYDAY=+1SA,+1SU;BYSETPOS=1,3

Answer 3

what you could try is to take advantage of the fact that bysetpos allows you to select within the year the selected instances of your rule, then you could limit the number of instances to the first week of the month (by setting the days of the month to the first 6 ones) to avoid the cases where month have more or less weeks, which then allows you to select the first and third instance in your year.

Which then gives:

DTSTART:20140320T060000Z FREQ=YEARLY;INTERVAL=2;WKST=MO;BYSETPOS=1,3;BYMONTH=2,9;BYMONTHDAY=1,2,3,4,5,6,7;BYDAY=SA,SU

which will be:

Sat 2014/Sept/6
Sat 2016/Feb/6
Sat 2016/Sep/3
...
Sun 2024/Sep/1

this was verified with dateutil-python and http://jkbr.github.io/,