Question

I have a collection in c#
For ex:

Collection<User> List = null;

I need to filter it based on sum parameters. so lets say i want to filter out users whos userID is between 1 to 100.

Please advice how i can do this in c#

Thanks
Amit

Answer 1

Assuming you’re using .NET 3.5 or higher, and you don’t need the filtering to be in place, just use LINQ:

var filteredUsers = unfilteredUsers.Where(u => u.UserID < 1 || u.UserID > 100)
                                   .ToList();

Note that this is filtering out users with IDs between 1 and 100 rather than filtering them in as per other answers.

If this doesn’t help, please clarify the question. (Out of interest, why are you using Collection<T> to start with?)

EDIT: If you really need a Collection<T> you can create one easily enough:

var filteredUsers = new Collection<User>
       (unfilteredUsers.Where(u => u.UserID < 1 || u.UserID > 100)
                       .ToList());

You could even add your own ToCollection extension method to make this simpler. But Collection<T> is usually meant to be the base class for more specific collection types (e.g. ObservableCollection<T>) – it’s odd to be constructing one directly. If your API is written in terms of Collection<T>, you should potentially change it to be written in terms of IList<T>, giving you more flexibility.