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Re: Best practice for group-adjacent with quasi-null

Subject: Re: Best practice for group-adjacent with quasi-null grouping key?
From: "Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 26 Apr 2016 18:44:02 -0000
Re:  Best practice for group-adjacent with quasi-null
On 26.04.2016 20:39, David Sewell dsewell@xxxxxxxxxxxx wrote:
(Following assumes XSLT 2.0)

I don't use the @group-adjacent form of <xsl:for-each-group> often
enough to be a master of it. I just ran into the problem that an empty
sequence is not allowed as the result of evaluating the group-adjacent
expression. Given data like

<contributor role="author">Joe Jones</contributor>
<contributor role="author">Mary Mitchell</contributor>
<contributor role="editor">Betty Berkeley</contributor>
<contributor role="editor">Peter Parker</contributor>

my first instinct was to use
  <xsl:for-each-group select="contributor" group-adjacent="@role">

but I got a run-time error because the @role is not always present in my
data. So I revised to

  <xsl:for-each-group select="contributor" group-adjacent="if (@role)
    then string(@role) else 'false'">

which give the desired results. But is there a better general strategy,
maybe using boolean false() as the grouping value, and then being sure
to cast current-grouping-key() as a string whenever a string comparison
is needed?

I would be inclined to simply use


unless you could have both <el role="">...</el> and <el>...</el> and
would need to distinguish them.

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