Counting unique XML element attributes using XSLT

Question

I've just started using XSLT and am trying to figure this out. Your help would be greatly appreciated.

Example XML file

<purchases>
    <item id = "1" customer_id = "5">
    </item>
    <item id = "2" customer_id = "5">
    </item>
    <item id = "7" customer_id = "4">
    </item>
</purchases>

Desired HTML Output:

<table>
    <tr><th>Customer ID</th><th>Number of Items Purchased</th></tr>
    <tr><td>5</td><td>2</td></tr>
    <tr><td>4</td><td>1</td></tr>
</table>

Customer with id number 5 has bought 2 items. Customer with id number 4 has bought 1 item.

Answer 1

XSLT 1.0 solution ....

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="html" indent="yes"/>

      <xsl:template match="/">
        <table>
          <xsl:apply-templates select="purchases/item"/>     
        </table>
      </xsl:template>

   <xsl:template match="item">
     <xsl:if test="not(
       preceding-sibling::*[@customer_id=current()/@customer_id]
       )">     
         <tr><td><xsl:value-of select="@customer_id"/></td>
           <td><xsl:value-of select="count(following-sibling::item
             [@customer_id=current()/@customer_id])+1"/></td>
         </tr> 
     </xsl:if>   
  </xsl:template>

</xsl:stylesheet>

Answer 2

If you want XSLT 2.0 then the following XSLT should do the trick:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xsl:output indent="yes"/>
    <xsl:template match="/purchases">
        <table>
            <tr>
                <th>Customer ID</th>
                <th>Number of Items Purchased</th>
            </tr>
            <xsl:for-each-group select="item" group-by="@customer_id">
                <tr>
                    <td>
                        <xsl:value-of select="current-grouping-key()"/>
                    </td>
                    <td>
                        <xsl:value-of select="count(current-group())"/>
                    </td>
                </tr>
            </xsl:for-each-group>
        </table>
    </xsl:template>
</xsl:stylesheet>

Answer 3

A possible Xslt 1.0 solution would be

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="html" indent="yes"/>

    <xsl:key name="kCustomer" match="item" use="@customer_id"/>

    <xsl:template match="/">
        <xsl:apply-templates />
    </xsl:template>

    <xsl:template match="purchases">
        <xsl:element name="table">
            <xsl:element name="tr">
                <xsl:element name="th">Customer ID</xsl:element>
                <xsl:element name="th">Number of Items Purchased</xsl:element>
                <xsl:for-each select="item[generate-id(.) = generate-id(key('kCustomer', @customer_id))]">
                    <xsl:variable name="total" select="count(/purchases/item[@customer_id=current()/@customer_id]/@id)" />
                    <xsl:element name="tr">
                        <xsl:element name="td">
                            <xsl:value-of select="./@customer_id" />
                        </xsl:element>
                        <xsl:element name="td">
                            <xsl:value-of select="$total" />
                        </xsl:element>
                    </xsl:element>
                </xsl:for-each>
            </xsl:element>
        </xsl:element>
    </xsl:template>

</xsl:stylesheet>

Adopted from Dimitres answer on How can I Group and sort based on sum .

---

As pointed out by Dimitre the purchases template can be simplified to

    <xsl:template match="purchases">
        <table>
            <tr>
                <th>Customer ID</th>
                <th>Number of Items Purchased</th>
            </tr>
            <xsl:for-each select="item[generate-id(.) = generate-id(key('kCustomer', @customer_id))]">
                <xsl:variable name="total" select="count(/purchases/item[@customer_id=current()/@customer_id]/@id)" />
                    <tr>
                        <td>
                            <xsl:value-of select="./@customer_id" />
                        </td>
                        <td>
                            <xsl:value-of select="$total" />
                        </td>
                    </tr>
            </xsl:for-each>
        </table>
    </xsl:template>