covariance

I have a dataframe with three columns: data$input, data$output and data$category. Both input and output are continuous numerics, and categories are discrete characters. I know ANCOVA is a method that analyzes the effect of input on output while controlling for the effect of category. However I could not find the exact command to do for this online. Here is a small example of how the data would look like: input output category 1 0.4 0.55 A 2 0.5 0.66 A 3 0.6 0.57 A 4 0.3 0.23 B 5 0.4 0.53 B 6 0.7 0.75 B 7 1.1 1.31 C 8 0.9 1.01 C 9 0.8 0.58 C 10 0.5 0.34 C What commands should I input to perform

I just need to use the covariant out generic type modifier again. I had a class with a generic type and wanted to add an out but VS told me that this is only possible on interfaces. But why can I use the out modifier only on an interface? I helped myself in creating an interface copy of my class but this seems a little bit strange to me to only have an interface so I can use this modifier. It's extremely difficult to ensure that the class's definition is in fact covariant. It is much easier for the compiler to ensure that the interface is in fact covariant. With a class, simply having a field

Following on from this question , can someone explain the following in Scala: class Slot[+T] (var some: T) { // DOES NOT COMPILE // "COVARIANT parameter in CONTRAVARIANT position" } I understand the distinction between +T and T in the type declaration (it compiles if I use T ). But then how does one actually write a class which is covariant in its type parameter without resorting to creating the thing unparametrized ? How can I ensure that the following can only be created with an instance of T ? class Slot[+T] (var some: Object){ def get() = { some.asInstanceOf[T] } } EDIT - now got this down

C# 4.0 .NET 4.5 Silverlight 5 It seems weird that I cant find the solution so need some help please. I have base class Base and derived class Child : Base. I have also helper class which has generic type to do specific work one EF entities Helper where T : EntityObject. Child does specific work with a specific entity MyEntity : EntityObject. So I tried: public class Base { protected Helper<EntityObject> helper; } public class Child : Base { public Child() { helper = new Helper<MyEntity>(); } } I would expect that more derived class must know about more specific generic parameter and I think