The comparer
argument in GroupBy
allows you to define equality for purposes of the object grouping. The comparer is a separate class that compares two like objects and returns true
if they are equal. The class, which needs to implement IComparer<CartItem>
, can be implemented like this:
class CartGroupComparer : IEqualityComparer<CartProduct>
{
public bool Equals(CartProduct x, CartProduct y)
{
return x.IDLocation == y.IDLocation
&& x.ShipMethods.OrderBy(x=>x)
.SequenceEqual(y.ShipMethods.OrderBy(x=>x));
}
public int GetHashCode(CartProduct obj)
{
return obj.IDLocation.GetHashCode()
^ obj.ShipMethods.Sum().GetHashCode();
}
}
(Note: for simplicity, this assumes that ShipMethods
will never be null.)
The Equals
method tests two items for equality; if equal, they will be added added to the same group. The GetHashCode
method must return an equal value for equal items, and a simple implementation is above.
You can use this comparer directly in your GroupBy
clause:
new CartProduct().GetExampleData()
.GroupBy(a => a, new CartGroupComparer());