Re: [xsl] Getting years from duration

[Martin Holmes <mholmes@xxxxxxx>]

On 13-06-07 08:57 PM, Michael Sokolov wrote:
> Yeah, that's a bit surprising.  But if you think about it there's a kind
> of logic to it -- once you start working with dayTimeDuration, there
> isn't any sensible way to know how many years that corresponded to
> (because of leap years/seconds, and the Gregorian switch-over year and
> so on), as you said yourself.

That's true, and it's interesting too. In one sense a duration 
abstracted from its start and end points loses some of its meaning.

> This will do what you want I think:
>
> let $d2 := year-from-date(xs:date("1674-11-08"))
> let $d1 := year-from-date(xs:date("1600-12-09"))
> return $d2 - $d1
>
> If you're concerned about rounding (ie you think that 11 years 11 months
> should be == 12 years), then you could add 6 months:
>
> let $d2 := year-from-date(xs:date("1674-11-08") +
> xs:yearMonthDuration("P6M"))
> let $d1 := year-from-date(xs:date("1600-12-09"))
> return $d2 - $d1

That works nicely. A function that would actually subtract the dates in 
a more methodical way -- subtracting days, "carrying" any overage to the 
months, then subtracting the months and carrying, then the years, could 
give a meaningful result in years, months and days, too. I'll hack that 
up tomorrow and see if it works. The day subtraction would have to be 
sensitive to month-length and leap-day.

Cheers,
Martin

> -Mike
>
> PS sorry for the XQuery instead of XSL, but the functions and datatypes
> are the same...
>
> On 6/7/2013 11:26 PM, Martin Holmes wrote:
> > We came up against what looked like a very simple XPath issue today,
> > and hit a brick wall with it. Given data that looks like this:
> >
> >         <person role="author">
> >           <persName>Milton, John</persName>
> >           <birth when="1600-12-09"/>
> >           <death when="1674-11-08"/>
> >         </person>
> >
> > we want to calculate the age of the person at death. So we thought:
> > subtract the death date from the birth date to get a duration, then
> > extract the years from the duration:
> >
> >   <xsl:template match="person">
> >
> >     <xsl:variable name="life" select="xs:date(death/@when) -
> > xs:date(birth/@when)"/>
> >
> >     <xsl:variable name="age" select="years-from-duration($life)"/>
> >
> >     <xsl:text>Age at death: </xsl:text>
> >     <xsl:value-of select="$age"/>
> >
> >   </xsl:template>
> >
> >
> > However, the only value we were able to get back, after trying all
> > manner of permutations and casts, was zero. It appears that what comes
> > back from the date subtraction (which I think uses the
> > op:subtract-dates() operator) is always an xs:dayTimeDuration, and
> > that cannot AFAIKS be manipulated into anything from which a year can
> > be extracted.
> >
> > It's always possible to get the number of days and divide by 365.25,
> > but it seems strange to have to do that. Given the range of date- and
> > duration-related functions, I'm sure there must be some better way of
> > getting the result. Does anyone know?
> >
> > This is using Saxon 9.4.0.6.
> >
> > Cheers,
> > Martin