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How to update all instances of an element in XDocument?

I have xml structure as below. How can I replace the element value of that is present everywhere in this structure? Is there a way to do this using Linq? Also, sometimes the structure could be different but there will always be Resource element so I need to look at all instances of Resource and not care about where it is present.
Thanks for any suggestions.
<Users>
<User>
<Number>123456</Number>
<ID>1</ID>
<Events>
<Event>
<ID>12</ID>
</Event>
</Events>
<Items>
<Item>
<ID>12</ID>
<Resource>Replace this value</Resource>
</Item>
<Item>
<ID>13</ID>
<Resource>Replace this value</Resource>
</Item>
<Item>
<ID>14</ID>
<Resource>Replace this value</Resource>
</Item>
</Items>
</User>
//More User elements where Resource needs to be updated
<User>
</User>
<User>
</User>
</Users>

Linq is a query language, so you can't directly use it to modify the value, but you can easily select all the Resource elements in the document with it and iterate/change them.
For example:
// or load from xml, however you have it
var xDoc = XDocument.Load(#"c:\temp\myxml.xml");
// iterate every Resource element
foreach (XElement element in xDoc.Descendants("Resource"))
element.Value = "Hello, world";
That will pick out every Resource element in the XML regardless of where it is in the hierarchy, which in your case, is what you need. If you needed to target it more specifically, you could either use an XPath expression or further Linq calls such as Element() which work on a single level of the hierarchy.

Loop each Items in c# using XElement

I am facing some difficulty in swapping the id attribute in the list of Items in a C# XDocument. The id is a reference.
Input:
<Items>
<Item base="book_bookref1_ref1">
<Name>Test1</Name>
<Ref>bookref1</Ref>
</Item>
<Item base="book_bookref1_ref2">
<Name>Test2</Name>
<Ref>bookref1</Ref>
</Item>
<Item base="book_bookref2_ref1">
<Name>Test3</Name>
<Ref>bookref2</Ref>
</Item>
<Item base="book_bookref2_ref2">
<Name>Test4</Name>
<Ref>bookref2</Ref>
</Item>
</Items>
Expected Output:
<Items>
<Item base="book_bookref1_ref1" id="book_bookref1_ref2">
<Name>Test1</Name>
<Ref>bookref1</Ref>
</Item>
<Item base="book_bookref1_ref2" id="book_bookref1_ref1">
<Name>Test2</Name>
<Ref>bookref1</Ref>
</Item>
<Item base="book_bookref2_ref1" id="book_bookref2_ref2">
<Name>Test3</Name>
<Ref>bookref2</Ref>
</Item>
<Item base="book_bookref2_ref2" id="bookref2_ref1">
<Name>Test4</Name>
<Ref>bookref2</Ref>
</Item>
</Items>
There is a tag <Ref> where one part of value ex:bookref1 is a reference for Base attribute book_bookref1_ref1 for the 1st and 2nd Item.
I need to write the 2nd 'id' to the 1st Item and write the 1st id to the 2nd Item in the loop. Similarly for the 3rd and 4th Item. There can be many but it's like a combination (1 & 2, 3 & 4, 5 & 6, etc).
The problem here is there can be multiple Items and there is no relation in the Item to map the Id attribute.
The code I'm using is loading XMLDocument into XDocument getting the Items in LINQ.
Var doc = XDocument.Load(xml)
var ItemsList
foreach(var itm in ItemsList)
{
// I'm stuck here. How do we get the id attribute value based on Ref tag?
}
Please let me know your suggestions.

Nothing in XML is impossible with a little LINQ (and MoreLinq, in this example):
var xdoc = XDocument.Parse(input);
foreach(var pair in xdoc.XPathSelectElements("Items/Item").Batch(2).ToArray())
{
pair[0].SetAttributeValue(XName.Get("id"), pair[1].Attribute(XName.Get("base")).Value);
pair[1].SetAttributeValue(XName.Get("id"), pair[0].Attribute(XName.Get("base")).Value);
}
This enumerates not each Item, not each Item pair (two elements in a batch). You only need to tweak this to decide what to do if an odd element remains at the end of the loop.
MoreLinq is for .Batch() extension method, but if you need, you can easily write it yourself.

xpath to return value from xml doc

I'm wondering if there is a way to do the following with one xpath expression:
I have an XML doc similar to this but with many 'results',
<result>
<id>1</id>
<name>joe</name>
</result>
<result>
<id>2</id>
<name>jim</name>
</result>
I'm passing a variable into a C# utility along with the xml, and want to return the name where the id = the variable.
I could loop through the xml until reach what I'm after but if there's a handy xpath way to do it I'm listening...
thanks

Assuming you have a root element in there like "results" that XPath can validate, and that you don't have any other nodes named "result"...
//result[id=1]/name
Or you could get the text outright, instead of it being returned in a node
//result[id=1]/name/text()
And if you want to make sure that there's only one result, you could surround it with parens and put a [1] after
(//result[id=1]/name/text())[1]
I would also recommend testing with one of the xpath test sites out there like this one, but beware that different xpath/xml parsers sometimes behave differently.

Convert node section into one line

i have xml document with a lot of items like this:
<item>
<key>
<unsignedShort>x</unsignedShort>
</key>
<value>
<unsignedShort>y</unsignedShort>
</value>
</item>
<item>
......
now i want that every section of it will look like this:
<item><key><unsignedShort>x</unsignedShort></key><value><unsignedShort>y</unsignedShort></value></item>

You would have to implement your own XmlWriter. XmlTextWriter allows you to use an unindented format, but that would result in the entire document being on one line. So, yeah, you'd have to roll your own, unless you're OK with the entire document sitting on one line.

What's the quickest (code execution) way to execute an XML reading?

I have to read the XML:
<items>
<item>
<prop1>value1</prop1>
<prop2>value2</prop2>
<prop3>value3</prop3>
</item>
<item>
<prop1>value1</prop1>
<prop2>value2</prop2>
<prop3>value3</prop3>
</item>
</items>
And put the values into a List<CLASS>.
Some options:
Use XMLSerializer to deserialize to a List
Use XMLDocument to read each item using SelectNodes with XPath and put the values into a List
Use XMLReader to read each node and put the values into a List
Other option...

By far the fastest that I have seen is to use XSD.exe to create an XSD and Class to go with it, then use serialization.

Another option would be to use LinqToXml.

If you're in dotnet, install the WCF starter pack. Then you'll have an option "Paste XML as Types", so you can cut the XML you're looking to serialize into the clipboard and paste it into code as a serializable type. Then you can just serialize the XML and get the values through the class.