XSLT根据分组的子节点值添加父节点

<students>
  <student>
    <name>John</name>
    <grade>A</grade>
  </student>
  <student>
    <name>Jane</name>
    <grade>B</grade>
  </student>
  <student>
    <name>Mike</name>
    <grade>A</grade>
  </student>
</students>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:key name="students-by-grade" match="student" use="grade" />

  <xsl:template match="/">
    <xsl:apply-templates select="students/student[generate-id() = generate-id(key('students-by-grade', grade)[1])]"/>
  </xsl:template>

  <xsl:template match="student">
    <group>
      <xsl:attribute name="grade">
        <xsl:value-of select="grade"/>
      </xsl:attribute>
      <xsl:apply-templates select="key('students-by-grade', grade)"/>
    </group>
  </xsl:template>

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

  <xsl:template match="name">
    <name>
      <xsl:value-of select="."/>
    </name>
  </xsl:template>
</xsl:stylesheet>

<group grade="A">
  <student>
    <name>John</name>
  </student>
  <student>
    <name>Mike</name>
  </student>
</group>
<group grade="B">
  <student>
    <name>Jane</name>
  </student>
</group>