How to query Min and Max from XML?

Question

<?xml version="1.0" encoding="utf-8"?>
<Customers>
   <Customer Id="1">
    <Name>rtertr</Name>
    <DOB>2010-12-12T00:00:00</DOB>
    <EMail>[email protected]</EMail>
  </Customer>
  <Customer Id="2">
    <Name>west</Name>
    <DOB>0001-01-01T00:00:00</DOB>
    <EMail>[email protected]</EMail>
   </Customer> 
  <Customer Id="3">
    <Name>west</Name>
    <DOB>0001-01-01T00:00:00</DOB>
    <EMail>[email protected]</EMail>
   </Customer> 
</Customers>

How to find Min and Max CustomerId from the above sample XML using LinQ to XML? For example for the above sample, Min should be 1 and Max should be 3

Answer 1

var doc = XDocument.Parse(...);

//.ToArray() so we only iterate once
var ids = doc.Root.Elements("Customer").Select(c => (int)c.Attribute("Id")).ToArray();
var minId = ids.Min();
var maxId = ids.Max();

As dtb´s comment says, this will iterate the array twice but only the xml document once. I feel this is a good compromise between readability and performance - at least when its not used in production code. Iterating the int array will be a small factor of the xml document iteration. The best solution is to only iterate the document once and keep track of the values along the way as dtb shows.

Answer 2

You can use the Min and Max extension methods:

var doc = XDocument.Parse("<Customers>...</Customers>");

var minId = doc.Root.Elements().Min(e => (int)e.Attribute("Id"));
var maxId = doc.Root.Elements().Max(e => (int)e.Attribute("Id"));

or the Aggregate extension method (iterating the XML document only once):

var doc = XDocument.Parse("<Customers>...</Customers>");

var result = doc.Root
                .Elements()
                .Select(e => (int)e.Attribute("Id"))
                .Aggregate(
                    Tuple.Create(int.MinValue, int.MaxValue),
                    (t, x) => Tuple.Create(Math.Max(t.Item1, x),
                                           Math.Min(t.Item2, x)));

var maxId = result.Item1;
var minId = result.Item2;