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<p>Hi Neil,</p>
<p>IMO duplicate instances generated from an RRULE should be handled
just like RRULE instances for which an RDATE exists. You merge
them into one. RFC 5545 speaks of a "recurrence set" and "a set is
a collection of distinct objects"
(<a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/Set_(mathematics)">https://en.wikipedia.org/wiki/Set_(mathematics)</a> ). So by
definition the recurrence set can not contain two equal instances.
This should answer 1 and 2.</p>
<p>Regarding 3, see the table on page 7
(<a class="moz-txt-link-freetext" href="https://tools.ietf.org/html/rfc7529#page-7">https://tools.ietf.org/html/rfc7529#page-7</a>)<br>
</p>
<p> o BYMONTH<br>
o SKIP (for invalid month only)<br>
o BYWEEKNO<br>
o BYYEARDAY<br>
o BYMONTHDAY<br>
o SKIP (for invalid day)<br>
o BYDAY<br>
o BYHOUR<br>
o BYMINUTE<br>
o BYSECOND<br>
o BYSETPOS<br>
o COUNT<br>
o UNTIL<br>
</p>
<p>It says that SKIP is applied before BYSETPOS. So In your example
2001-02-30 and 2001-02-31 would both wrap around to 2001-03-01
which becomes the 2nd instance of this particular set (even though
it's in the next month), and also happens to be the first instance
of the "March Set". So in this case 3 instances are merged into
one.<br>
</p>
<p>That's my interpretation and how I intended to implemented it.
However, I've just noticed that we return 2001-03-01 twice, which
is not correct. I'll fix that.<br>
</p>
<p>Cheers,</p>
<p>Marten<br>
</p>
<div class="moz-cite-prefix">Am 19.10.18 um 06:23 schrieb Neil
Jenkins:<br>
</div>
<blockquote type="cite"
cite="mid:ab09c5ef-8184-4959-8b1b-26befdb84ea7@sloti22d1t06">
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<div>Hi everyone,<br>
</div>
<div><br>
</div>
<div>I'm trying to extend the <a
href="https://tools.ietf.org/html/draft-ietf-calext-jscalendar-08#section-4.3.1"
moz-do-not-send="true">JSCalendar recurrence rule expansion
algorithm</a> to accommodate <a
href="https://tools.ietf.org/html/rfc7529#section-4.1"
moz-do-not-send="true">RFC7529</a> and support RSCALE and
SKIP. The former is easy, the latter seems to be a real pain.
One big problem I'm running into is that the RFC seems to be
quite under-specified when it comes to any kind of edge cases.
So, can anyone help answer a few questions (presume <code
style="border-radius:3px;border:1px solid #ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">DTSTART=20010201</code>
for all of these):<br>
</div>
<div><br>
</div>
<ol>
<li>What happens if I generate duplicates due to SKIP; should
they be removed, or considered separate occurrences? e.g. <code
style="border-radius:3px;border:1px solid #ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">RSCALE=GREGORIAN;FREQ=YEARLY;BYMONTH=2,3;BYMONTHDAY=1,31;SKIP=FORWARD</code>.
I presume that should not generate two instances of 2001-03-01
despite this being the result of <code
style="border-radius:3px;border:1px solid #ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">BYMONTH=2;BYMONTHDAY=31;SKIP=FORWARD</code>
as well as <code style="border-radius:3px;border:1px solid
#ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">BYMONTH=3;BYMONTHDAY=1</code>.<br>
</li>
<li>What about if the duplicates occur in different periods,
e.g. <code style="border-radius:3px;border:1px solid
#ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">RSCALE=GREGORIAN;FREQ=MONTHLY;BYMONTHDAY=1,31;SKIP=FORWARD</code>
– should they still be removed?<br>
</li>
<li>How does this interact with <code
style="border-radius:3px;border:1px solid #ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">BYSETPOS</code>?
Are the duplicates removed before or after applying this? For
example, <code style="border-radius:3px;border:1px solid
#ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">RSCALE=GREGORIAN;FREQ=MONTHLY;BYMONTHDAY=1,30,31;BYSETPOS=1,2;SKIP=FORWARD</code>
– this might evaluate to 2001-02-01, 2001-02-30, 2001-02-31.
We apply bySetPos and dedup (in either order) and get
2001-02-01, 2001-03-01. OK, now we continue to March. is
2001-03-01 considered for part of the <code
style="border-radius:3px;border:1px solid #ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">BYSETPOS</code> (so
you get just 2001-03-30)? Or because it's already been
generated from the Feb candidates due to the SKIP rule, is it
eliminated before applying <code
style="border-radius:3px;border:1px solid #ccc;padding:1px
3px;background:#f6f6f6;font-family:menlo,consolas,monospace;font-size:90%;">BYSETPOS</code> (so
you get 2001-03-30 and 2001-03-31)?<br>
</li>
</ol>
<div><br>
</div>
<div>Looking forward to being enlightened on this,<br>
</div>
<div><br>
</div>
<div>Neil.</div>
<br>
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<pre class="moz-signature" cols="72">--
Marten Gajda
CEO
dmfs GmbH
Schandauer Straße 34
01309 Dresden
GERMANY
phone: +49 177 4427167
email: <a class="moz-txt-link-abbreviated" href="mailto:marten@dmfs.org">marten@dmfs.org</a>
Managing Director: Marten Gajda
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VAT Reg. No.: DE303248743</pre>
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