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On 25/02/2011 15:29, David Lee wrote:
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<div class="WordSection1">
<p class="MsoNormal">Today I ran into yet a new hole in my
xquery knowledge. (I guess I’m a sponge !)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I needed to check if a value was numeric or
not. I found the functx function<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a moz-do-not-send="true"
href="http://www.xqueryfunctions.com/xq/functx_is-a-number.html">http://www.xqueryfunctions.com/xq/functx_is-a-number.html</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The code is interesting :<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Courier New"; color: black;"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Courier New"; color: black;">define function
is-a-number <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Courier New"; color: black;"> ( $value as
xdt:anyAtomicType? ) as xs:boolean {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Courier New"; color: black;"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Courier New"; color: black;"> fn:string(fn:number($value))
!= 'NaN'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Courier New"; color: black;"> }<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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</blockquote>
This code returns false if the input is NaN, which is interesting
though not wrong - despite the name, NaN is a member of the numeric
value space.<br>
<blockquote cite="mid:025501cbd500$c178b220$446a1660$@calldei.com"
type="cite">
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m wondering why this hand-standing ? Why
cant I compare to NaN directly ?<o:p></o:p></p>
<p class="MsoNormal">Is there no literal constructor for NaN ? I
cant find any … and my obvious attempts fail like<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> If( number(“abc”) eq NaN )
… </p>
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</blockquote>
Because comparison to NaN always yields false.<br>
<blockquote cite="mid:025501cbd500$c178b220$446a1660$@calldei.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Its just strange to me to have a value
which can be returned by a function which you cant construct …<o:p></o:p></p>
<br>
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</blockquote>
You can construct it using xs:double('NaN') or xs:float('NaN')<br>
<br>
Michael Kay<br>
Saxonica<br>
<br>
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