I have a problem using Linq to order a structure like this :
public class Person
{
public int ID { get; set; }
public List Attribu
Why don't you use a key-value dictionary instead of your List<PersonAttribute> ? It would suit better, i think, and make everything else easier.
Update - like this:
public class Person
{
public Dictionary<string, string> Attributes = new Dictionary<string,string>();
}
List<Person> people = new List<Person>();
Person rebecca = new Person();
rebecca.Attributes["Age"] = "32";
rebecca.Attributes["FirstName"] = "Rebecca";
rebecca.Attributes["LastName"] = "Johnson";
rebecca.Attributes["Gender"] = "Female";
people.Add(rebecca);
var PeopleInAgeOrder = people.OrderBy(p => p.Attributes["Age"]);
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)));
}
}
Some cases you need to consider:
If you create this extension methods class:
public static class ListExtenstions
{
public static List<Person> OrderList(this List<Person> list, string attributeName, PersonAttribute defaultAttribute)
{
return OrderList(list, attributeName, defaultAttribute, x => x);
}
public static List<Person> OrderList<T>(this List<Person> list, string attributeName, PersonAttribute defaultAttribute, Func<string, T> convertion)
{
return list.OrderBy(x => convertion((x.Attributes.FirstOrDefault(y => y.Name == attributeName) ?? defaultAttribute).Value)).ToList();
// Query Syntax
//return
// (from p in list
// let attribute = p.Attributes.FirstOrDefault(a => a.Name == attributeName) ?? defaultAttribute
// orderby attribute.Value
// select p).ToList();
}
}
You can then sort the list correctly in this manner:
List<Person> persons = ...
...
PersonAttribute defaultAttribute = new PersonAttribute() { Value = "0" };
var ordered = persons.OrderList("Age", defaultAttribute, x => Convert.ToInt32(x));
This will give correct sorting order.
If the attribute will always be present you could remove defaultAttribute
.
To sort on 'Name' just use:
List<Person> persons = ...
...
PersonAttribute defaultAttribute = new PersonAttribute() { Value = String.Empty };
var ordered persons.OrderList("Name", defaultAttribute);
This is assuming that Attribute class implement IComparable or has a nice ToString function (i hope).
var list = personList.OrderBy(p => p.Attributes.FirstOrDefault(a => a.Name == "Age"))
Otherwise the syntax gets more convoluted:
var list = personList
.OrderBy(p =>
p.Attributes.FirstOrDefault(a => a.Name == "Age") == null ?
"" : p.Attributes.First(a => a.Name == "Age").Value
);
I also assume that you have one value for each key - otherwise you'd need to have smarter code... ;-)
I know this is an old post, but I thought I'd post a comparer I found a while ago in case anyone else needs it.
public class GenericComparer<T> : IComparer<T>
{
public string SortExpression { get; set; }
public int SortDirection { get; set; } // 0:Ascending, 1:Descending
public GenericComparer(string sortExpression, int sortDirection)
{
this.SortExpression = sortExpression;
this.SortDirection = sortDirection;
}
public GenericComparer() { }
#region IComparer<T> Members
public int Compare(T x, T y)
{
PropertyInfo propertyInfo = typeof(T).GetProperty(SortExpression);
IComparable obj1 = (IComparable)propertyInfo.GetValue(x, null);
IComparable obj2 = (IComparable)propertyInfo.GetValue(y, null);
if (SortDirection == 0)
{
return obj1.CompareTo(obj2);
}
else return obj2.CompareTo(obj1);
}
#endregion
}
Usage
List<MyObject> objectList = GetObjects(); /* from your repository or whatever */
objectList.Sort(new GenericComparer<MyObject>("ObjectPropertyName", (int)SortDirection.Descending));
dropdown.DataSource = objectList;
dropdown.DataBind();
You could overload the constructor to accept the SortDirection enum. I didn't do this because the class is in a library without a reference to System.Web.
I'd imagine that you're getting an exception where one item doesn't have an age attribute. I tried the below code, and it worked fine - I'm guessing your data is a bit off, as pointed out by other posters. Anyway, the below works fine...
List<Person> personList = new List<Person>();
Random rand = new Random();
//generate 50 random persons
for (int i = 0; i < 50; i++)
{
Person p = new Person();
p.Attributes = new List<PersonAttribute>();
p.Attributes.Add(new PersonAttribute() { ID = 8, Name = "Age", Value = rand.Next(0, 100).ToString() });
p.Attributes.Add(new PersonAttribute() { ID = 10, Name = "Name", Value = rand.Next(0, 100).ToString() });
personList.Add(p);
}
var finalList = personList.OrderBy(c => c.Attributes.Find(a => a.Name == "Age").Value).ToList();