C# – Sort a List using query expressions

c++expressionlinqsorting

I have a problem using Linq to order a structure like this :

public class Person
{
    public int ID { get; set; }
    public List<PersonAttribute> Attributes { get; set; }
}

public class PersonAttribute
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string Value { get; set; }
}

A person might go like this:

PersonAttribute Age = new PersonAttribute { ID = 8, Name = "Age", Value = "32" };
PersonAttribute FirstName = new PersonAttribute { ID = 9, Name = "FirstName", Value = "Rebecca" };
PersonAttribute LastName = new PersonAttribute { ID = 10, Name = "LastName", Value = "Johnson" };
PersonAttribute Gender = new PersonAttribute { ID = 11, Name = "Gender", Value = "Female" };

I would like to use LINQ projection to sort a list of persons ascending by the person attribute of my choice, for example, sort on Age, or sort on FirstName.

I am trying something like

string mySortAttribute = "Age"
PersonList.OrderBy(p => p.PersonAttribute.Find(s => s.Name == mySortAttribute).Value);

But the syntax is failing me. Any clues?

Best Solution

OrderBy is a LINQ extension that produces a new sequence. To order the existing sequence you need to add an extension method or two... then you can use:

PersonList.Sort(p => p.Attributes.Find(
  s => s.Name == mySortAttribute).Value);

public static class ListExtensions {
  public static void Sort<TSource, TValue>(
    this List<TSource> source,
    Func<TSource, TValue> selector)
  {
    var comparer = Comparer<TValue>.Default;
    source.Sort((x, y) => comparer.Compare(selector(x), selector(y)));
  }
  public  static void SortDescending<TSource, TValue>(
    this List<TSource> source,
    Func<TSource, TValue> selector)
  {
    var comparer = Comparer<TValue>.Default;
    source.Sort((x, y) => comparer.Compare(selector(y), selector(x)));
  }
}
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