Question

I want to write an extension method to filter all the people with towns in a people object with the towns in shop object

class people
    string name
    string town

class shops
    string category
    string town

i know i can write

var x = from p in people
        from s in shops
        where p.town == s.town

but i would like to know how to write

var x = from p in people.FilterByTown(p) or FilterByTown(p => p.town) or however it is!!

where FilterByTown is the extension method and all the magic works in there and the object i pass in gets compared with the shop object.

It needs to work with different objects being fed to the method

Hope that all makes sense, the code above is obviously pseudo!

Answer 1

Assuming you have 2 collections people and shops you can write this:

List<People> people = ...
List<Shops> shops = ...

IEnumerable<People> Filter(this IEnumerable<People> people, IEnumerable<Shops> shops){
var result = people.Where(p=>shops.Any(s=>s.town == p.town));
return result;
}

If you want to sort all classes by some arbitrary property you can try this version:

public static IEnumerable<T1> Filter<T1, T2>(
    this IEnumerable<T1> one, 
    IEnumerable<T2> two, string property)
        {
           var result = one.Where(o => two.Any(t =>
               o.GetType().GetProperty(property).
               GetValue(o, null).Equals(t.GetType().
               GetProperty(property).GetValue(t, null))));
           return result;
        }

Of course you need to be sure that property is valid and both objects have it.