Delete duplicates using Lambda

Delete duplicates using Lambda

I need some help using a lambda expression to remove duplicate entries in
my Entity Framework context. I have a table with the following columns:
Id, DateOfIncident, Description, EmployeeId, IncidentTypeId, and
IsAttendanceIncident
I want to remove duplicate entries where DateOfIncident, EmployeeID,
IncidentTypeID and IsAttendanceIncident are the same. I do want to keep
one entry. I know how to do this using a Stored Procedure with CTE in SQL,
but I cannot figure out how to accomplish this task using a Lambda
expression.
This code returns a list excluding my duplicates, but now how do I go
about removing those duplicates that are not in this list ?
var query = db.Incidents.Where(x => x.IsAttendanceIncident ==
"Y").GroupBy(x => new { x.EmployeeId, x.DateOfIncident,
x.IsAttendanceIncident })
.Select(x => x.FirstOrDefault());