Get index of object in a list using Linq [duplicate]

Answer 1

You don't need to use LINQ, you can use FindIndex of List<T>:

int index = customers.FindIndex(c => c.ID == 150);

Answer 2

Linq to Objects has overloaded Select method

customers.Select((c,i) => new { Customer = c, Index = i })
         .Where(x => x.Customer.ID == 150)
         .Select(x => x.Index);

Keep in mind, that you should have in-memory List<Customer> to use this Linq to Objects method.