[Rd] S3/S4 classes performance comparison

[Eric Lecoutre]

Hi R-devel,

If you did read my survey on Rhelp about reporting, you may have seen that 
I am implementing a way to handle outputs for R (mainly target output 
destinations: xHTML and TeX).
In fact: I does have something that works for basic objects, entirely done 
with S4 classes, with the results visible at:
http://www.stat.ucl.ac.be/ROMA/sample.htm
http://www.stat.ucl.ac.be/ROMA/sample.pdf

To achieve this goal, I do use intermediary objects that would reprensent 
the structure of the output. Thus I defined classes for Vector, Tables, 
Rows, Cells, Sections, and so on. Most of those structure are recursive.
Then, at a firts attemps, a matrix would be represented as a Table 
containing Rows containg Cells containing Vectors, which finally is easy to 
export and which makes easy the customisation (if you need to insert a 
footnote within a cell for example).
I know that this intermediary layout would be far more easier to handle at 
C level, but I dont have any C skill for that...

One of my problem is that this consumes a lot of memory/computation time.
Too much, indeed...
20 sec. to export data(iris) on my PIV 3.2 Ghz 1Go RAM, which is not 
acceptable.

I was intending to do start properly, as starting from scratch new code. I 
did write everything using S4 classes.
Doing a simple test reveals crucial efficiency differences between S3 and 
S4 classes.

Here is the test:

---

### S3 CLASSES

S3content <- function(obj=NULL,add1=NULL,add2=NULL,type="",...){
         out <- list(content=obj,add1=add2,add2=add2,type=type)
         class(out) <- "S3Content"
         return(out)
}

S3vector <- function(vec,...){
   out <- S3content(obj=vec,type="Vector",...)
   class(out) <- "S3Vector"
   return(out)
}


### S4 classes

setClass("S4content",representation(content="ANY",add1="ANY",add2="ANY",type="character"))

S4content <- function(obj=NULL,add1=NULL,add2=NULL,type="",...){
   new("S4content",content=obj,add1=add1,add2=add2,type=type)
}

S4vector <- function(vec,...){
   new("S4content",type="vector",content=vec,...)
}

### Now the test
 > test <- rnorm(10000)
 > gc()
          used (Mb) gc trigger (Mb)
Ncells 169135  4.6     531268 14.2
Vcells  75260  0.6     786432  6.0
 > (system.time(lapply(test,S3vector)))
[1] 0.17 0.00 0.19   NA   NA
 > gc()
          used (Mb) gc trigger (Mb)
Ncells 169136  4.6     531268 14.2
Vcells  75266  0.6     786432  6.0
 > (system.time(lapply(test,S4vector)))
[1] 15.08  0.00 15.13    NA    NA
-----

There is here a factor higher than 80!

Is there something trivial I did overlook?
Is this 80 factor normal?

Is it still recommended (recommendable...) to use S4 classes when 
considered that?



Eric

Eric Lecoutre
UCL /  Institut de Statistique
Voie du Roman Pays, 20
1348 Louvain-la-Neuve
Belgium

tel: (+32)(0)10473050
lecoutre at stat.ucl.ac.be
http://www.stat.ucl.ac.be/ISpersonnel/lecoutre

If the statistics are boring, then you've got the wrong numbers. -Edward 
Tufte