I know I can call linq's Except and specify a custom IEqualityComparer, but implementing a new Comparer class for each data type seems like an overkill for this purpose. Can I use a lambda expression to provide the equality function, like when I use Where or other LINQ functions?
If I can't, is there an alternative?
Can you not use a .Where with a lambda that filters out your required values?
Example as requested:
static void Main(string[] args)
{
var firstCustomers = new[] { new Customer { Id = 1, Name = "Bob" }, new Customer { Id = 2, Name = "Steve" } };
var secondCustomers = new[] { new Customer { Id = 2, Name = "Steve" }, new Customer { Id = 3, Name = "John" } };
var customers = secondCustomers.Where(c => !firstCustomers.Select(fc => fc.Id).Contains(c.Id));
}
public class Customer
{
public int Id { get; set; }
public string Name { get; set; }
}
Here's something simple I whipped up:
public class CustomComparer<TSource, TCompareType> : IEqualityComparer<TSource> where TSource : class
{
private readonly Func<TSource, TCompareType> getComparisonObject;
public CustomComparer(Func<TSource,TCompareType> getComparisonObject)
{
if (getComparisonObject == null) throw new ArgumentNullException("getComparisonObject");
this.getComparisonObject = getComparisonObject;
}
/// <summary>
/// Determines whether the specified objects are equal.
/// </summary>
/// <returns>
/// true if the specified objects are equal; otherwise, false.
/// </returns>
/// <param name="x">The first object of type <paramref name="T"/> to compare.
/// </param><param name="y">The second object of type <paramref name="T"/> to compare.
/// </param>
public bool Equals(TSource x, TSource y)
{
if (x == null)
{
return (y == null);
}
else if (y == null)
{
return false;
}
return EqualityComparer<TCompareType>.Default.Equals(getComparisonObject(x), getComparisonObject(y));
}
/// <summary>
/// Returns a hash code for the specified object.
/// </summary>
/// <returns>
/// A hash code for the specified object.
/// </returns>
/// <param name="obj">The <see cref="T:System.Object"/> for which a hash code is to be returned.
/// </param><exception cref="T:System.ArgumentNullException">The type of <paramref name="obj"/> is a reference type and <paramref name="obj"/> is null.
/// </exception>
public int GetHashCode(TSource obj)
{
return EqualityComparer<TCompareType>.Default.GetHashCode(getComparisonObject(obj));