Test first subnode from node.

Question

XML:

    <mode>
        <submode>1</submode>
        <submode>2</submode>
        <submode>3</submode>
        <submode>4</submode>
        <submode>5</submode>
        <submode>6</submode>
        <submode>7</submode>
    </mode>
    <mode>
        <submode>7</submode>
        <submode>8</submode>
        <submode>9</submode>
        <submode>10</submode>
        <submode>11</submode>
        <submode>12</submode>
        <submode>13</submode>
    </mode>
    <mode>
        <submode>14</submode>
        <submode>15</submode>
        <submode>16</submode>
        <submode>17</submode>
        <submode>18</submode>
        <submode>19</submode>
        20</submode>
    </mode>   

How to test first <submode> from each <mode> (i need get numbers: 1, 7, 14) in such construction:

<xsl:template match="submode">
    <xsl:if test="(parent::mode) and (...what?...)">
        ...
    </xsl:if>
    ...
</xsl:template>

I do not understand how use position() here.

Answer 1

Your <xsl:template match= should read "mode/submode[1]".

Then you'd have the first submode of every mode.

Answer 2

It is not generally true that

position() = 1

evaluates to true() if the current node has a parent mode and the current node is the first submode child of its parent.

position() specifies the position of the current node-list and this is defined in a different way, depending on how the select attribute of <xsl:apply-templates> is specified.

For example (assuming that the provided XML has a top element that is the parent of the mode elements), if the template was selected when processingthe following:

<xsl:apply-templates select="/*/mode/submode[. = 3]"/>

then

position() = 1

is true only for the 3rd submode child of the first mode element.

One correct answer:

parent::mode and not(preceding-sibling::submode)

Or, recommended:

Have a separate template:

<xsl:template match="mode/submode[1]">

In this case no code within template is necessary to check if the current node is the first submode child -- this is already known to be so.

Answer 3

To count the number of submodes in the previous mode if and only if this is the first submode of the current mode, and avoid duplicating code between <xsl:template match="submode"> and <xsl:template match="submode[1]">:

<!-- Special processing for first submode -->
<xsl:template match="submode[1]">
    <xsl:variable name="previousSubmodes" 
                  select="count(../preceding-sibling::mode/submode)"/>

    <!-- ... Do stuff with count ... -->

    <!-- Perform regular submode processing -->
    <xsl:call-template name="submode"/>

</xsl:template>

<!-- Regular processing for submodes -->
<xsl:template match="submode" name="submode">
    <!--  ... Do whatever ... -->
</xsl:template>

Alternatively, you can do the count processing from the template for mode instead. That way, you will not need any special processing for the first submode.

<xsl:template match="mode">
    <!-- ... Other processing ... -->

    <xsl:variable name="previousSubmodes" 
                  select="count(preceding-sibling::mode/submode)"/>

    <!-- ... Do stuff with count ... -->

    <!-- Handle submodes; could use select="node()|@*" instead to process 
         everything, not just submodes  -->
    <xsl:apply-templates select="submode"/>

</xsl:template>

<xsl:template match="submode">
    <!--  ... Do whatever ... -->
</xsl:template>