Edit

Share via

How to find child elements based on position (LINQ to XML)

This article shows how to use XPathSelectElements to find elements based on element position – for example, to find the second element, or the third through the fifth. It also shows two ways to use LINQ to XML query to do the same thing.

There are two approaches to writing this LINQ to XML query in a lazy way. You can use the Skip and Take operators, or you can use the Where overload that takes an index. When you use the Where overload, you use a lambda expression that takes two arguments. The following example shows both methods of selecting based on position.

Example: Find the second through the fourth Test elements

This example finds the second through the fourth Test element in the Sample XML file: Test configuration. The result is a collection of elements.

The XPath expression is Test[position() >= 2 and position() <= 4].

XElement testCfg = XElement.Load("TestConfig.xml");

// LINQ to XML query
IEnumerable<XElement> list1 =
    testCfg
    .Elements("Test")
    .Skip(1)
    .Take(3);

// LINQ to XML query
IEnumerable<XElement> list2 =
    testCfg
    .Elements("Test")
    .Where((el, idx) => idx >= 1 && idx <= 3);

// XPath expression
IEnumerable<XElement> list3 =
  testCfg.XPathSelectElements("Test[position() >= 2 and position() <= 4]");

if (list1.Count() == list2.Count() &&
    list1.Count() == list3.Count() &&
    list1.Intersect(list2).Count() == list1.Count() &&
    list1.Intersect(list3).Count() == list1.Count())
    Console.WriteLine("Results are identical");
else
    Console.WriteLine("Results differ");
foreach (XElement el in list1)
    Console.WriteLine(el);

Dim testCfg As XElement = XElement.Load("TestConfig.xml")

' LINQ to XML query
Dim list1 As IEnumerable(Of XElement) = _
    testCfg.Elements("Test").Skip(1).Take(3)

'LINQ to XML query
Dim list2 As IEnumerable(Of XElement) = _
    testCfg.Elements("Test"). _
    Where(Function(ByVal el, ByVal idx) idx >= 1 And idx <= 3)

' XPath expression
Dim list3 As IEnumerable(Of XElement) = _
    testCfg.XPathSelectElements("Test[position() >= 2 and position() <= 4]")

If list1.Count() = list2.Count() And _
       list1.Count() = list3.Count() And _
       list1.Intersect(list2).Count() = list1.Count() And _
       list1.Intersect(list3).Count() = list1.Count() Then

    Console.WriteLine("Results are identical")
Else
    Console.WriteLine("Results differ")
End If

For Each el As XElement In list1
    Console.WriteLine(el)
Next

This example produces the following output:

Results are identical
<Test TestId="0002" TestType="CMD">
  <Name>Find succeeding characters</Name>
  <CommandLine>Examp2.EXE</CommandLine>
  <Input>abc</Input>
  <Output>def</Output>
</Test>
<Test TestId="0003" TestType="GUI">
  <Name>Convert multiple numbers to strings</Name>
  <CommandLine>Examp2.EXE /Verbose</CommandLine>
  <Input>123</Input>
  <Output>One Two Three</Output>
</Test>
<Test TestId="0004" TestType="GUI">
  <Name>Find correlated key</Name>
  <CommandLine>Examp3.EXE</CommandLine>
  <Input>a1</Input>
  <Output>b1</Output>
</Test>

See also