XSLT: Sort by the lower of 2 values

Question

I have some XML that is formatted as follows:

<products>
  <product>
    <name>Product 1</name>
    <price>
      <orig>15</orig>
      <offer>10</offer>
    </price>
  </product>
  <product>
    <name>Product 2</name>
    <price>
      <orig>13</orig>
      <offer>12</offer>
    </price>
  </product>
  <product>
    <name>Product 3</name>
    <price>
      <orig>11</orig>
    </price>
  </product>
</products>

I need to sort the products using XSLT 1.0 (in either ascending or descending order) based on their current price. My difficulty lies in the fact that I need to sort on the lower of the two possible price values <orig> and <offer> if they both exist.

For the above example the correct ordering would be:

• Product 1 (lowest value = 10)
• Product 3 (lowest value = 11)
• Product 2 (lowest value = 12)

Any help would be much appreciated, as I can't seem to find a similar question through the search.

Answer 1

(answer updated to include thoughts on both XSLT 1.0 and 2.0)

I. XSLT 1.0:

Note that XSLT 1.0 does not have a built-in equivalent to min(); assuming your parser supports EXSLT, you can make use of its math:min() function to achieve a solution quite similar to the below XSLT 2.0 variant.

---

II. XSLT 2.0:

Here is a solution that makes use of the XPath 2.0 aggregation function min().

When this XSLT 2.0 solution:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
  <xsl:output omit-xml-declaration="no" indent="yes"/>
  <xsl:strip-space elements="*"/>

  <xsl:template match="node()|@*">
    <xsl:copy>
      <xsl:apply-templates select="node()|@*"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="products">
    <products>
      <xsl:apply-templates select="product">
        <xsl:sort select="min(price/offer|price/orig)"
          data-type="number" order="ascending" />
      </xsl:apply-templates> 
    </products>
  </xsl:template>

</xsl:stylesheet>

..is applied to the provided XML:

<products>
  <product>
    <name>Product 1</name>
    <price>
      <orig>15</orig>
      <offer>10</offer>
    </price>
  </product>
  <product>
    <name>Product 2</name>
    <price>
      <orig>13</orig>
      <offer>12</offer>
    </price>
  </product>
  <product>
    <name>Product 3</name>
    <price>
      <orig>11</orig>
    </price>
  </product>
</products>

..the wanted result is produced:

<?xml version="1.0" encoding="UTF-8"?>
<products>
   <product>
      <name>Product 1</name>
      <price>
         <orig>15</orig>
         <offer>10</offer>
      </price>
   </product>
   <product>
      <name>Product 3</name>
      <price>
         <orig>11</orig>
      </price>
   </product>
   <product>
      <name>Product 2</name>
      <price>
         <orig>13</orig>
         <offer>12</offer>
      </price>
   </product>
</products>

Answer 2

I. There is a general and pure XSLT 1.0 solution -- as simple as this:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:template match="node()|@*">
  <xsl:copy>
   <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
 </xsl:template>

 <xsl:template match="/*">
  <products>
   <xsl:apply-templates select="*">
    <xsl:sort data-type="number" select=
    "price/*[not(../* &lt; .)]"/>
   </xsl:apply-templates>
  </products>
 </xsl:template>
</xsl:stylesheet>

---

II. If price has other children in addition to offer and orig -- in this case the general solution I. above (as well as the other two answers to this question) doesn't work correctly.

Here is a correct solution for this case:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:template match="node()|@*">
  <xsl:copy>
   <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
 </xsl:template>

 <xsl:template match="/*">
  <products>
   <xsl:apply-templates select="*">
    <xsl:sort data-type="number" select=
    "sum(price/orig[not(../offer &lt;= .)])
   +
     sum(price/offer[not(../orig &lt; .)])
    "/>
   </xsl:apply-templates>
  </products>
 </xsl:template>
</xsl:stylesheet>

---

III. If we know that offer never exceeds orig:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:template match="node()|@*">
  <xsl:copy>
   <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
 </xsl:template>

 <xsl:template match="/*">
  <products>
   <xsl:apply-templates select="*">
    <xsl:sort data-type="number" 
         select="price/offer | price/orig[not(../offer)]"/>
   </xsl:apply-templates>
  </products>
 </xsl:template>
</xsl:stylesheet>

IV. Verification:

All three transformations above, when applied to the provided XML document:

<products>
  <product>
    <name>Product 1</name>
    <price>
      <orig>15</orig>
      <offer>10</offer>
    </price>
  </product>
  <product>
    <name>Product 2</name>
    <price>
      <orig>13</orig>
      <offer>12</offer>
    </price>
  </product>
  <product>
    <name>Product 3</name>
    <price>
      <orig>11</orig>
    </price>
  </product>
</products>

produce the wanted, correct result:

<products>
   <product>
      <name>Product 1</name>
      <price>
         <orig>15</orig>
         <offer>10</offer>
      </price>
   </product>
   <product>
      <name>Product 3</name>
      <price>
         <orig>11</orig>
      </price>
   </product>
   <product>
      <name>Product 2</name>
      <price>
         <orig>13</orig>
         <offer>12</offer>
      </price>
   </product>
</products>

Solution II is the only of the three that still produces the correct result when applied on this XML document (added a minAcceptable child to price):

<products>
  <product>
    <name>Product 1</name>
    <price>
      <orig>15</orig>
      <offer>10</offer>
      <minAcceptable>8</minAcceptable>
    </price>
  </product>
  <product>
    <name>Product 2</name>
    <price>
      <orig>13</orig>
      <offer>12</offer>
      <minAcceptable>6</minAcceptable>
    </price>
  </product>
  <product>
    <name>Product 3</name>
    <price>
      <orig>11</orig>
      <minAcceptable>7</minAcceptable>
    </price>
  </product>
</products>

Do note that none of the other answers processes this XML document correctly.