====== Symbolic objects in R ======

<code>
> setClass("interval",representation(min="numeric",max="numeric"))
[1] "interval"
> getClass("interval")
Class "interval" [in ".GlobalEnv"]

Slots:
                      
Name:      min     max
Class: numeric numeric
> a <- new("interval",min=2,max=3)
> a
An object of class "interval"
Slot "min":
[1] 2

Slot "max":
[1] 3

> x <- vector("list",2)
> x
[[1]]
NULL

[[2]]
NULL

> T <- data.frame(u=x,v=x)
> T
data frame with 0 columns and 0 rows
>
# 17. december 2011
# http://rwiki.sciviews.org/doku.php?id=tips:data-frames:list_in_data.frame
> df <- data.frame (normal.column = "a",
+   the.list = I(list ("1st.row" = list ("x" = 8, "unit" = "mm"),
+                      "2nd.row" = "blabla") ))
> df
        normal.column the.list
1st.row             a    8, mm
2nd.row             a   blabla
> 

> T <- data.frame(u = c(7,4), v = I(list( "prva"=a, "druga"=a )))
> T
Error in as.character.default(<S4 object of class "interval">) : 
  no method for coercing this S4 class to a vector
> A <- c(4,5,6); B <- c(7,1,3)
> T <- data.frame(u = c(7,4), v = I(list(A,B)))
> T
  u       v
1 7 4, 5, 6
2 4 7, 1, 3
> T[2,2]
[[1]]
[1] 7 1 3

> Z <- data.frame(u = c(7,4), v = I(list( "prva"=a, "druga"=a )))
> Z[2,1]
[1] 4
> Z[2,2]
$druga
An object of class "interval"
Slot "min":
[1] 2

Slot "max":
[1] 3

> b <- new("interval",min=5,max=9)
> Z[2,2] <- b
> Z[2,2]
$druga
An object of class "interval"
Slot "min":
[1] 5

Slot "max":
[1] 9

> dim(Z)
[1] 2 2
</code>

===== Refs =====

  * http://blog.datacamp.com/data-table-cheat-sheet/ ; https://github.com/Rdatatable/data.table/wiki ; https://github.com/Rdatatable/data.table/wiki/Articles ; https://s3.amazonaws.com/assets.datacamp.com/img/blog/data+table+cheat+sheet.pdf
  * http://stat.ethz.ch/R-manual/R-patched/library/base/html/class.html
  * http://stat.ethz.ch/R-manual/R-devel/library/methods/html/refClass.html
  * http://stat.stanford.edu/~jmc4/pub.html
  * http://stat.stanford.edu/~jmc4/classInheritance.pdf
  * http://www.ibm.com/developerworks/linux/library/l-r3/
  * http://www.stat.wisc.edu/~deepayan/SIBS2005/slides/objects.pdf
  * http://en.wikipedia.org/wiki/Object-oriented_programming
  * http://www.omegahat.org/
  * http://www.uwyo.edu/mdillon/hor.html
  * http://zoonek2.free.fr/UNIX/48_R/02.html