Question

How can I create an easy helper method to get an int array from a collection of objects?

The idea would be have a method which receive a collection of “User” class:

public class User { 
    public int UserId {get;set;}
    public string UserName {get;set;}
}

And filter this collection to get an int array of unique UserIds.

List<int> repeatedUserIds = (from item in list 
                             select item.UserId).ToList();
List<int> uniqueUserIds = ((from n in repeatedUserIds 
                             select n).Distinct()).ToList();

Is there a way to create a clever method for this purpose?

Answer 1

You could create an extension method:

public int[] GetUniqueIds<T>(this IEnumerable<T> items, Func<T, int> idSelector)
{
    return items.Select(idSelector).Distinct().ToArray();
}

And use it like this:

int[] uniqueUserIds = list.GetUniqueIds(u => u.UserId);