Re: [xsl] Best practice for group-adjacent with quasi-null grouping key?

["Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

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

   group-adjacent="string(@role)"

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


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