XSLT Get First Element Node

Question

<SMRCRLT_XML>
 <AREA>
  <DETAILS>
   <DETAIL_REQUIREMENT>
    <RULE_REQUIREMENT>
     <DETAIL_REQUIREMENT>
      <COURSE_ROWSET>
       <COURSE_SET>
        <COURSE_AREA>TESTSELECT</COURSE_AREA>
        <COURSE_KEY_RULE>1200</COURSE_KEY_RULE>
        <COURSE_SET>A</COURSE_SET>
        <COURSE_SUBSET>1</COURSE_SUBSET>
        <COURSE_SUBJ_CODE>CHEM</COURSE_SUBJ_CODE>
        <COURSE_CRSE_NUMB_LOW>345A</COURSE_CRSE_NUMB_LOW>
       </COURSE_SET>
      </COURSE_ROWSET>
     </DETAIL_REQUIREMENT>
     <DETAIL_REQUIREMENT>
      <COURSE_ROWSET>
       <COURSE_SET>
        <COURSE_KEY_RULE>1200</COURSE_KEY_RULE>
        <COURSE_SET>A</COURSE_SET>
        <COURSE_SUBSET>2</COURSE_SUBSET>
        <COURSE_SUBJ_CODE>CHEM</COURSE_SUBJ_CODE>
        <COURSE_CRSE_NUMB_LOW>476A</COURSE_CRSE_NUMB_LOW>
       </COURSE_SET>
      </COURSE_ROWSET>
     </DETAIL_REQUIREMENT>
     <DETAIL_REQUIREMENT>
      <COURSE_ROWSET>
       <COURSE_SET>
        <COURSE_AREA>TESTSELECT</COURSE_AREA>
        <COURSE_KEY_RULE>1200</COURSE_KEY_RULE>
        <COURSE_SET>A</COURSE_SET>
        <COURSE_SUBSET>3</COURSE_SUBSET>
        <COURSE_SUBJ_CODE>PHIL</COURSE_SUBJ_CODE>
        <COURSE_CRSE_NUMB_LOW>432</COURSE_CRSE_NUMB_LOW>
       </COURSE_SET>
      </COURSE_ROWSET>
     </DETAIL_REQUIREMENT>
     <DETAIL_REQUIREMENT>
      <COURSE_ROWSET>
       <COURSE_SET>
        <COURSE_AREA>TESTSELECT</COURSE_AREA>
        <COURSE_KEY_RULE>1200</COURSE_KEY_RULE>
        <COURSE_SET>B</COURSE_SET>
        <COURSE_SUBSET>4</COURSE_SUBSET>
        <COURSE_SUBJ_CODE>PHIL</COURSE_SUBJ_CODE>
        <COURSE_SUBJ_DESC>Philosophy</COURSE_SUBJ_DESC>
        <COURSE_CRSE_NUMB_LOW>433</COURSE_CRSE_NUMB_LOW>
       </COURSE_SET>
      </COURSE_ROWSET>
     </DETAIL_REQUIREMENT>
     <DETAIL_REQUIREMENT>
      <COURSE_ROWSET>
       <COURSE_SET>
        <COURSE_AREA>TESTSELECT</COURSE_AREA>
        <COURSE_KEY_RULE>1200</COURSE_KEY_RULE>
        <COURSE_SET>B</COURSE_SET>
        <COURSE_SUBSET>5</COURSE_SUBSET>
        <COURSE_SUBJ_CODE>ZOOL</COURSE_SUBJ_CODE>
        <COURSE_CRSE_NUMB_LOW>321</COURSE_CRSE_NUMB_LOW>
       </COURSE_SET>
      </COURSE_ROWSET>
     </DETAIL_REQUIREMENT>
     <DETAIL_REQUIREMENT>
      <COURSE_ROWSET>
       <COURSE_SET>
        <COURSE_AREA>TESTSELECT</COURSE_AREA>
        <COURSE_KEY_RULE>1200</COURSE_KEY_RULE>
        <COURSE_SET>B</COURSE_SET>
        <COURSE_SUBSET>6</COURSE_SUBSET>
        <COURSE_SUBJ_CODE>BIOC</COURSE_SUBJ_CODE>
        <COURSE_CRSE_NUMB_LOW>456</COURSE_CRSE_NUMB_LOW>
       </COURSE_SET>
      </COURSE_ROWSET>
     </DETAIL_REQUIREMENT>
    </RULE_REQUIREMENT>
   </DETAIL_REQUIREMENT>
  </DETAILS>
 </AREA>
</SMRCRLT_XML>

I am trying to get the first element from the XML for each COURSE_SET, but it returns all the values. Can someone please help. This is my template that I applied:

<xsl:apply-templates select="//SMRCRLT_XML/AREA/DETAILS/DETAIL_REQUIREMENT/RULE_REQUIREMENT/DETAIL_REQUIREMENT/COURSE_ROWSET/COURSE_SET[COURSE_AREA='TESTSELECT' and COURSE_KEY_RULE='1200'][1]"/>

The results I am getting are:

CHEM345A
PHIL432
PHIL433
ZOOL321
BIOC456

The result I am looking for is CHEM 345A and then PHIL433

Answer 1

The efficient way to handle a task like this in XSLT 1.0 is to use Muenchian grouping, like this:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>
  <xsl:key name="kSet" match="COURSE_ROWSET/COURSE_SET" use="COURSE_SET" />

  <xsl:template match="/">
    <root>
      <xsl:apply-templates
        select="//COURSE_ROWSET/COURSE_SET[generate-id() = 
                  generate-id(key('kSet', COURSE_SET)[1])]" />
    </root>
  </xsl:template>

  <xsl:template match="COURSE_ROWSET/COURSE_SET">
    <item>
      <xsl:value-of select="concat(COURSE_SUBJ_CODE, COURSE_CRSE_NUMB_LOW)"/>
    </item>
  </xsl:template>
</xsl:stylesheet>

When this XSLT is applied to your sample input, the result is:

<root>
  <item>CHEM345A</item>
  <item>PHIL433</item>
</root>

Answer 2

You have several problems here.

First, the [1] in your XPath expression is filtering the XPath value by requiring that the COURSE_SET elements selected be the first child of their parent. Without that [1], your XPath expression reads:

//SMRCRLT_XML
/AREA
/DETAILS
/DETAIL_REQUIREMENT
/RULE_REQUIREMENT
/DETAIL_REQUIREMENT
/COURSE_ROWSET
/COURSE_SET
[COURSE_AREA='TESTSELECT' and COURSE_KEY_RULE='1200']

But every COURSE_SET that matches that path expression is the first child of its parent. (The only COURSE_SET elements which are not first children are children of COURSE_SET, not children of COURSE_ROWSET.)

The second problem is that it appears, judging by your question and your attempt at formulating the XPath expression you want, that you would like the courses to be grouped somehow (at first I thought you might want them grouped by department but now I expect you want them grouped by the value of the nested COURSE_SET element, which in your example has values A or B), so that by selecting the first COURSE_SET in some suitable context you can get the first course listed for each group. But the XML you show doesn't in fact group the courses by department or by course set; it provides a flat list of courses with no groupings at all. There are no elements here for which CHEM 345A and PHIL 433 are the first courses.

If your design calls for the courses to be grouped by department or course set, then your data source is not providing the data you want, and you will want to fix it.

If on the other hand you're stuck with this XML and want to use XPath to try to provide the structure that your data source is not capable of providing, then you don't want "the first element for each COURSE_SET", you want "each COURSE_SET which is in a department (or a COURSE_SET) different from the immediately preceding COURSE_SET". And your XPath expression can be something like

//COURSE_ROWSET/COURSE_SET
  [not(COURSE_SET eq preceding::COURSE_SET[1])]

Your third problem is that your XML seems to be too fond of using the same name for different constructs (one set of COURSE_SET elements each of which contains a description of a course, with department and course number and so on, and a second set of COURSE_SET elements which contain the strings 'A' and 'B', two sets of DETAIL_REQUIREMENT with different content, and so on. It's confusing for people not familiar with the data, and it will make every single discussion of detail an opportunity for miscommunication and error.