improving code to find nodes with using attributename and node - asp.net

Question

I have following xml:
<TextWithNodes><Node id="0" />astralis<Node id="8" /> <Node id="9" />ltd<Node id="12" />
<Node id="14" />{<Node id="15" />DOCUMENT<Node id="23" />}<Node id="24" /> <Node id="25" />{<Node id="26" />TYPE<Node id="30" />}<Node id="31" />EX-<Node id="34" />10<Node id="36" />.<Node id="37" />12<Node id="39" /> <Node id="40" />{<Node id="41" />SEQUENCE<Node id="49" />}<Node id="50" />3<Node id="51" /> <Node id="52" />{<Node id="53" />FILENAME<Node id="61" />}<Node id="62" />e<Node id="63" />300201<Node id="69" />_<Node id="70" />ex<Node id="72" />10<Node id="74" />-<Node id="75" />12<Node id="77" />.<Node id="78" />txt<Node id="81" /> </TextWithNodes>
and I need to pick node from Id 25 to id 75. It is a portion of XML. Original XML is very long.
I am using following code:
Dim reader As XmlTextReader = New XmlTextReader(System.Web.HttpContext.Current.Server.MapPath("~/App_Data/gate_xml_output.xml"))
reader.WhitespaceHandling = WhitespaceHandling.None
Dim xmlDoc As XmlDocument = New XmlDocument()
'Load the file into the XmlDocument
xmlDoc.Load(reader)
'Close off the connection to the file.
reader.Close()
Dim nodeList As XmlNodeList = xmlDoc.SelectNodes("//TextWithNodes/node()[preceding-sibling::Node[#id=" & startNode & "] and following-sibling::Node[#id=" & endNode & "]]")
Dim sb As StringBuilder = New StringBuilder
For Each childNode As XmlNode In nodeList
If childNode.Value IsNot Nothing Then
sb.Append(childNode.Value & " ")
End If
Next
' read the text between these nodes
ExtractText = sb.ToString
It is working but It is very slow. Any alternative of getting this data from XML ?
Please suggest.
Thanks

Answer 1

Explore Linq to XML; it should be quicker: http://msdn.microsoft.com/en-us/library/bb387098.aspx
Also good info here: http://www.hookedonlinq.com/LINQtoXML5MinuteOverview.ashx
There's ton of info out there.
Here's an article about performance comparison with xmldoc and xmlreader: http://www.nearinfinity.com/blogs/joe_ferner/performance_linq_to_sql_vs.html
and another: http://msdn.microsoft.com/en-us/library/bb387048.aspx
+1

Answer 2

You could do it with XPath. Like this:
Dim sb As New StringBuilder()
Dim document As New XPathDocument("C:\testfile2.xml")
Dim navigator As XPathNavigator = document.CreateNavigator()
Dim iterator As XPathNodeIterator = navigator.Select("yourPath")
While iterator.MoveNext()
sb.Append(iterator.Current.Value)
End While
You can find more information here

Answer 3

The evaluation of this XPath expression has only O(N) complexity (linear) vs. O(N^2) for your original XPath expression:
/*/Node[#id >= 15 and not(#id > 75)]
This selects any Node element that is a child of the top element of the XML document and the value of whose id attribute is between the two specified lower and upper limits: respectively 15 and 75.
Here we assume that the values of the id attributes of Node elements are monotonously increasing -- exactly as in the provided XML document.
XSLT - based verification:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:copy-of select=
"/*/Node[#id >= 15 and not(#id > 75)]"/>
</xsl:template>
</xsl:stylesheet>
when this transformation is performed on the provided XML document:
<TextWithNodes>
<Node id="0" />astralis
<Node id="8" />
<Node id="9" />ltd
<Node id="12" />
<Node id="14" />{
<Node id="15" />DOCUMENT
<Node id="23" />}
<Node id="24" />
<Node id="25" />{
<Node id="26" />TYPE
<Node id="30" />}
<Node id="31" />EX-
<Node id="34" />10
<Node id="36" />.
<Node id="37" />12
<Node id="39" />
<Node id="40" />{
<Node id="41" />SEQUENCE
<Node id="49" />}
<Node id="50" />3
<Node id="51" />
<Node id="52" />{
<Node id="53" />FILENAME
<Node id="61" />}
<Node id="62" />e
<Node id="63" />300201
<Node id="69" />_
<Node id="70" />ex
<Node id="72" />10
<Node id="74" />-
<Node id="75" />12
<Node id="77" />.
<Node id="78" />txt
<Node id="81" />
</TextWithNodes>
the XPath expression is evaluated and the selected nodes are output:
<Node id="15"/>
<Node id="23"/>
<Node id="24"/>
<Node id="25"/>
<Node id="26"/>
<Node id="30"/>
<Node id="31"/>
<Node id="34"/>
<Node id="36"/>
<Node id="37"/>
<Node id="39"/>
<Node id="40"/>
<Node id="41"/>
<Node id="49"/>
<Node id="50"/>
<Node id="51"/>
<Node id="52"/>
<Node id="53"/>
<Node id="61"/>
<Node id="62"/>
<Node id="63"/>
<Node id="69"/>
<Node id="70"/>
<Node id="72"/>
<Node id="74"/>
<Node id="75"/>