How to group by custom types with linq

Question

I have this class

public class Item
{
       public Coordinate coordinate { get; set; }
        ...
        ...
}

With Coordinate being def

Answer 1

You've shown the Equals implementation, but not GetHashCode. You need to override both (and in a consistent way) for grouping to work.

Sample GetHashCode implementation:

public override int GetHashCode()
{
    int hash = 23;
    hash = hash * 31 + Latitude.GetHashCode();
    hash = hash * 31 + Longitude.GetHashCode();
    return hash;
}

Note that comparing float values for exact equality is always somewhat risky - but I'd at least expect your unit tests to pass, given that they're not performing any calculations.

Answer 2

There is an overload to the GrouBy method that takes an IEqualityComparer as a parameter, but is there the equivalent using the group clause?

You can always group by an anonymous type, if you just want a quick inline solution and aren't worried about hitting the exact type for the keys:

var grouped =
  from it in items 
  group it by new {it.Coordinate.Latitude, it.Coordinate.Longitude};