After learning the basics of XSLT one often wonders how to filter the XML data to returns data that contains a search string or has a value greater then or less than another value. To do this in XSL Stylesheets you can use take advantage of XPath in your xsl:foreach elements. Lets assume we have the following xml data as I used in my previous XSLT sorting article modified so that the year and publisher values are now attributes and not sub elements.

     
	Patrick Rothfuss
	
   
     
	Trudi Canavan
	
   
     
	Trudi Canavan
	
   
     
	Jim Butcher
	
   
     
	Jim Butcher
	
   
     
	Brandon Sanderson
	
   

Next we’ll create a basic XSL Stylesheet that will simply display our data in a table.

    
    
    

  

   

       
Title
       
Author
       
Publisher
       
Year
   
  
 
  

   
	  
       

       

       

       

    
   
  

This stylesheet will give us the following output:

Now for applying our filters, you will notice that in the xsl:for-each we use the select attribute to define the XML nodes to iterate over. This value books/book is an XPath value saying all elements of path books > book. To filter we simply modify the XPath. For example lets say we want all books published after 2008. To do this we would use the following XPath books/book[(number(@year) > 2008)]. This string says select all book elements that have an attribute of year greater then 2008. The xsl:for-each statement would look like the following.

This would render the following output:

If we wanted our filter to be even more complicated we could use multiple attributes or child elements in are select statement for example we could only want books published after 2008 and only display authors that contain the letter i. Doing this we would make use of the XSL function contains to compare strings as well as the and keyword to join are statements. The finished XPath would be books/book[(number(@year) > 2007) and contains(author, ‘i’)] with the output being the following XHTML.

That is pretty much all there is to it. There are many functions available to utilize in your XPath query strings and can be referenced here. For further details also visit the w3schools website’s XPath tutorial