#' Coefficient of determination class
 #'
 #' Coefficient of determination (r-squared).
 #' @export r_squared
 
 r_squared<-setClass(
   "r_squared",
   contains='metric',
   prototype = list(name='r squared',
     type="regression"
   )
 )
 
 #' @export
 setMethod(f="calculate",
   signature=c('r_squared'),
   definition=function(obj,Y,Yhat)
   {
     SSR  = sum((Yhat-mean(Y))^2)
     SSE  = sum((Y-Yhat)^2)
     SSTO = sum((Y-mean(Y))^2)
 
     R2=1-(SSE/SSTO)
 
     obj@value=R2
 
     return(obj)
   }
 )