new tasks

Task/Classes/R/classes-2.r

@@ -0,0 +1,24 @@
+setClass("circle",
+   representation(
+      radius="numeric",
+      centre="numeric"),
+   prototype(
+      radius=1,
+      centre=c(0,0)))
+#Instantiate class with some arguments
+circS4 <- new("circle", radius=5.5)
+#Set other data slots (properties)
+circS4@centre <- c(3,4.2)
+
+#Define a method
+setMethod("plot", #signature("circle"),
+   signature(x="circle", y="missing"),
+   function(x, ...)
+   {
+      t <- seq(0, 2*pi, length.out=200)
+      #Note the use of @ instead of $
+      plot(x@centre[1] + x@radius*cos(t),
+         x@centre[2] + x@radius*sin(t),
+         type="l", ...)
+   })
+plot(circS4)

Task/Classes/R/classes.r

@@ -0,0 +1,13 @@
+#You define a class simply by setting the class attribute of an object
+circS3 <- list(radius=5.5, centre=c(3, 4.2))
+class(circS3) <- "circle"
+
+#plot is a generic function, so we can define a class specific method by naming it plot.classname
+plot.circle <- function(x, ...)
+{
+   t <- seq(0, 2*pi, length.out=200)
+   plot(x$centre[1] + x$radius*cos(t),
+      x$centre[2] + x$radius*sin(t),
+      type="l", ...)
+}
+plot(circS3)