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I'm trying to transform the following XML:

<products>
  <product>1</product>
  <product>1</product>
  <product>1</product>
  <product>1</product>
  <product>1</product>
  <product>1</product>
  <product>1</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
  <product>2</product>
</products>

to:

<products>
  <product>1</product>
  <product>2</product>
</products>

using:

<products>
<xsl:for-each-group select="/products" group-by="product">
  <product><xsl:value-of select="product" /></product>
</xsl:for-each-group>
</products>

What am I doing wrong?  Basically I want something similar to 'GROUP BY'
 in SQL.
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