Re: [xsl] XSLT 2.0/XPath 2.0 Date arithmetic

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Dear Charles,

The new time-and-date data types work very well for this stuff. First 
contrive a way to cast your date string to an honest date value (this 
will involve munging its format a bit to the normative 'YYYY-MM-DD' 
arrangement, then casting it). At that point you can simply 
"subtract" days from it. Date arithmetic allows the addition and 
subtraction of dayTimeDuration values from dates (and times): very handy.

Here's a snippet of code that does something not dissimilar:

<xsl:variable name="day" select="xdt:dayTimeDuration('P1D')"/>

<xsl:variable name="thisMonday"
   select="(for $d in (0 to 6) return
     ($today - ($d * $day)))[format-date(.,'[F]')='Monday']"/>

Given a date value $today, $thisMonday is bound to the 
immediately-preceding Monday. That is, if $today is (a date value) 
'2006-05-17', the select expression here iterates over $today and the 
immediately-preceding six days, and returns those members of the 
sequence that turn out to be Mondays (which happens to be 
'2006-05-15'; but if $today were 2006-06-01, $thisMonday would be 2006-05-29).

The short version: if $today = xs:date($string) (and $string is in 
the form of "2006-05-17"), then

$tMinus1 = ($today - xdt:dayTimeDuration('P1D'))

I'm finding both Mike Kay's XPath 2.0 book, and Jeni Tennison's 
Learning XSLT 2.0 book, to be invaluable for figuring all this out. 
Honestly, I don't know what we'd do without them.

Cheers,
Wendell

At 05:29 PM 5/17/2006, you wrote:
> Given a parameter, let's call it "today" in the form of this string 
> "20060517", how do I create a variable, let's call it "tMinus1" such 
> that it represents a day earlier than "20060517", that would be 
> "20060516". So long as "$today" isn't the first day of a month, a 
> simple subtraction and followed by a type cast that I don't grasp 
> would do the trick.
>
> What I'm looking for is guidance on date arithmetic.
>
> Thanks.
>
> --
> Charles Knell
> cknell@xxxxxxxxxx - email


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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