Object Oriented Design(s) in R
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Romain François presented different object oriented design approaches in R including lexical scoping, S3 classes, S4 classes, reference (R5) classes, C++ classes, and Protocol Buffers. He used a bank account example to demonstrate how to represent account data and operations like deposits and withdrawals in each approach. Reference classes provide an easy to use alternative to S4 classes that also uses pass by reference semantics. C++ classes and Protocol Buffers allow integrating C++ and protobuf defined objects with R.
![> open.account <- function(total, overdraft = 0.0){
+ deposit <- function(amount) {
+ if( amount < 0 )
+ stop( "deposits must be positive" )
+ total <<- total + amount
+ }
+ withdraw <- function(amount) {
+ if( amount < 0 )
+ stop( "withdrawals must be positive" )
+ if( total - amount < overdraft )
+ stop( "you cannot withdraw that much" )
+ total <<- total - amount
+ }
+ balance <- function() {
+ total
+ }
+ list( deposit = deposit, withdraw = withdraw,
+ balance = balance )
+ }
> romain <- open.account(500)
> romain$balance()
[1] 500
> romain$deposit(100)
> romain$withdraw(200)
> romain$balance()
[1] 400](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-5-320.jpg)
![S3 classes
Example use:
> romain <- Account( 500 )
> balance( romain )
[1] 500
> romain <- deposit( romain, 100 )
> romain <- withdraw( romain, 200 )
> balance( romain )
[1] 400](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-9-320.jpg)
![S4 classes
> setClass( "Account",
+ representation(
+ balance = "numeric",
+ overdraft = "numeric"
+ ),
+ prototype = prototype(
+ balance = 0.0,
+ overdraft = 0.0
+ ),
+ validity = function(object){
+ object@balance > object@overdraft
+ }
+ )
[1] "Account"
> setGeneric( "balance",
+ function(x) standardGeneric( "balance" )
+ )
[1] "balance"
> setMethod( "balance", "Account",
+ function(x) x@balance
+ )
[1] "balance"](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-12-320.jpg)
![S4 classes
> setGeneric( "deposit",
+ function(x, amount) standardGeneric( "deposit" )
+ )
[1] "deposit"
> setMethod( "deposit",
+ signature( x = "Account", amount = "numeric" ),
+ function(x, amount){
+ new( "Account" ,
+ balance = x@balance + amount,
+ overdraft = x@overdraft
+ )
+ }
+ )
[1] "deposit"](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-13-320.jpg)
![S4 classes
> romain <- new( "Account", balance = 500 )
> balance( romain )
[1] 500
> romain <- deposit( romain, 100 )
> romain <- withdraw( romain, 200 )
> balance( romain )
[1] 400](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-14-320.jpg)
![Outline Fil rouge lexical scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers
> Account <- setRefClass( "Account_R5",
+ fields = list(
+ balance = "numeric",
+ overdraft = "numeric"
+ ),
+ methods = list(
+ withdraw = function( amount ){
+ if( amount < 0 )
+ stop( "withdrawal must be positive" )
+ if( balance - amount < overdraft )
+ stop( "overdrawn" )
+ balance <<- balance - amount
+ },
+ deposit = function(amount){
+ if( amount < 0 )
+ stop( "deposits must be positive" )
+ balance <<- balance + amount
+ }
+ )
+ )
> x <- Account$new( balance = 10.0, overdraft = 0.0 )
> x$withdraw( 5 )
> x$deposit( 10 )
> x$balance
[1] 15
Romain François Objects @ Chiacgo R User Group/Oct 2010](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-17-320.jpg)
![Outline Fil rouge lexical scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers
Real pass by reference :
> borrow <- function( x, y, amount = 0.0 ){
+ x$withdraw( amount )
+ y$deposit( amount )
+ invisible(NULL)
+ }
> romain <- Account$new( balance = 5000, overdraft = 0.0 )
> dirk <- Account$new( balance = 3, overdraft = 0.0 )
> borrow( romain, dirk, 2000 )
> romain$balance
[1] 3000
> dirk$balance
[1] 2003
Romain François Objects @ Chiacgo R User Group/Oct 2010](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-18-320.jpg)
![Outline Fil rouge lexical scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers
Adding a method dynamically to a class :
> Account$methods(
+ borrow = function(other, amount){
+ deposit( amount )
+ other$withdraw( amount )
+ invisible(NULL)
+ }
+ )
> romain <- Account$new( balance = 5000, overdraft = 0.0 )
> dirk <- Account$new( balance = 3, overdraft = 0.0 )
> dirk$borrow( romain, 2000 )
> romain$balance
[1] 3000
> dirk$balance
[1] 2003
Romain François Objects @ Chiacgo R User Group/Oct 2010](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-19-320.jpg)
![C++ classes
Exposing to R through Rcpp modules:
RCPP_MODULE(yada){
class_<Account>( "Account")
// expose the field
.field_readonly( "balance", &Account::balance )
// expose the methods
.method( "withdraw", &Account::withdraw )
.method( "deposit", &Account::deposit ) ;
}
Use it in R:
> Account <- yada$Account
> romain <- Account$new()
> romain$deposit( 10 )
> romain$withdraw( 2 )
> romain$balance
[1] 8](https://image.slidesharecdn.com/romainfrancois-101021083417-phpapp01/85/Object-Oriented-Design-s-in-R-22-320.jpg)
Object Oriented Design(s) in R
- 1. Object Oriented Design(s) in R Romain François romain@r-enthusiasts.com Chicago Local R User Group, Oct 27th , Chicago.
- 2. Outline Lexical Scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers
- 3. Fil rouge: bank account example Data: - The balance - Authorized overdraft Operations: - Open an account - Get the balance - Deposit - Withdraw .
- 5. > open.account <- function(total, overdraft = 0.0){ + deposit <- function(amount) { + if( amount < 0 ) + stop( "deposits must be positive" ) + total <<- total + amount + } + withdraw <- function(amount) { + if( amount < 0 ) + stop( "withdrawals must be positive" ) + if( total - amount < overdraft ) + stop( "you cannot withdraw that much" ) + total <<- total - amount + } + balance <- function() { + total + } + list( deposit = deposit, withdraw = withdraw, + balance = balance ) + } > romain <- open.account(500) > romain$balance() [1] 500 > romain$deposit(100) > romain$withdraw(200) > romain$balance() [1] 400
- 6. S3 classes
- 7. S3 classes Any R object with a class attribute Very easy Very dangerous Behaviour is added through S3 generic functions > Account <- function( total, overdraft = 0.0 ){ + out <- list( balance = total, overdraft = overdraft ) + class( out ) <- "Account" + out + } > balance <- function(x){ + UseMethod( "balance" ) + } > balance.Account <- function(x) x$balance
- 8. S3 classes > deposit <- function(x, amount){ + UseMethod( "deposit" ) + } > deposit.Account <- function(x, amount) { + if( amount < 0 ) + stop( "deposits must be positive" ) + x$balance <- x$balance + amount + x + } > withdraw <- function(x, amount){ + UseMethod( "withdraw" ) + } > withdraw.Account <- function(x, amount) { + if( amount < 0 ) + stop( "withdrawals must be positive" ) + if( x$balance - amount < x$overdraft ) + stop( "you cannot withdraw that much" ) + x$balance <- x$balance - amount + x + }
- 9. S3 classes Example use: > romain <- Account( 500 ) > balance( romain ) [1] 500 > romain <- deposit( romain, 100 ) > romain <- withdraw( romain, 200 ) > balance( romain ) [1] 400
- 10. S4 classes
- 11. S4 classes Formal class definition Validity checking Formal generic functions and methods Very verbose, both in code and documentation
- 12. S4 classes > setClass( "Account", + representation( + balance = "numeric", + overdraft = "numeric" + ), + prototype = prototype( + balance = 0.0, + overdraft = 0.0 + ), + validity = function(object){ + object@balance > object@overdraft + } + ) [1] "Account" > setGeneric( "balance", + function(x) standardGeneric( "balance" ) + ) [1] "balance" > setMethod( "balance", "Account", + function(x) x@balance + ) [1] "balance"
- 13. S4 classes > setGeneric( "deposit", + function(x, amount) standardGeneric( "deposit" ) + ) [1] "deposit" > setMethod( "deposit", + signature( x = "Account", amount = "numeric" ), + function(x, amount){ + new( "Account" , + balance = x@balance + amount, + overdraft = x@overdraft + ) + } + ) [1] "deposit"
- 14. S4 classes > romain <- new( "Account", balance = 500 ) > balance( romain ) [1] 500 > romain <- deposit( romain, 100 ) > romain <- withdraw( romain, 200 ) > balance( romain ) [1] 400
- 16. Reference (R5) classes Real S4 classes: formalism, dispatch, ... Passed by Reference Easy to use
- 17. Outline Fil rouge lexical scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers > Account <- setRefClass( "Account_R5", + fields = list( + balance = "numeric", + overdraft = "numeric" + ), + methods = list( + withdraw = function( amount ){ + if( amount < 0 ) + stop( "withdrawal must be positive" ) + if( balance - amount < overdraft ) + stop( "overdrawn" ) + balance <<- balance - amount + }, + deposit = function(amount){ + if( amount < 0 ) + stop( "deposits must be positive" ) + balance <<- balance + amount + } + ) + ) > x <- Account$new( balance = 10.0, overdraft = 0.0 ) > x$withdraw( 5 ) > x$deposit( 10 ) > x$balance [1] 15 Romain François Objects @ Chiacgo R User Group/Oct 2010
- 18. Outline Fil rouge lexical scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers Real pass by reference : > borrow <- function( x, y, amount = 0.0 ){ + x$withdraw( amount ) + y$deposit( amount ) + invisible(NULL) + } > romain <- Account$new( balance = 5000, overdraft = 0.0 ) > dirk <- Account$new( balance = 3, overdraft = 0.0 ) > borrow( romain, dirk, 2000 ) > romain$balance [1] 3000 > dirk$balance [1] 2003 Romain François Objects @ Chiacgo R User Group/Oct 2010
- 19. Outline Fil rouge lexical scoping S3 classes S4 classes Reference (R5) classes C++ classes Protocol Buffers Adding a method dynamically to a class : > Account$methods( + borrow = function(other, amount){ + deposit( amount ) + other$withdraw( amount ) + invisible(NULL) + } + ) > romain <- Account$new( balance = 5000, overdraft = 0.0 ) > dirk <- Account$new( balance = 3, overdraft = 0.0 ) > dirk$borrow( romain, 2000 ) > romain$balance [1] 3000 > dirk$balance [1] 2003 Romain François Objects @ Chiacgo R User Group/Oct 2010
- 20. C++ classes
- 21. C++ classes class Account { public: Account() : balance(0.0), overdraft(0.0){} void withdraw( double amount ){ if( balance - amount < overdraft ) throw std::range_error( "no way") ; balance -= amount ; } void deposit( double amount ){ balance += amount ; } double balance ; private: double overdraft ; } ;
- 22. C++ classes Exposing to R through Rcpp modules: RCPP_MODULE(yada){ class_<Account>( "Account") // expose the field .field_readonly( "balance", &Account::balance ) // expose the methods .method( "withdraw", &Account::withdraw ) .method( "deposit", &Account::deposit ) ; } Use it in R: > Account <- yada$Account > romain <- Account$new() > romain$deposit( 10 ) > romain$withdraw( 2 ) > romain$balance [1] 8
- 23. Protocol Buffers
- 24. Protocol Buffers Define the message type, in Account.proto : package foo ; message Account { required double balance = 1 ; required double overdraft = 2 ; } Load it into R with RProtoBuf: > require( RProtoBuf ) > loadProtoFile( "Account.proto" ) Use it: > romain <- new( foo.Account, + balance = 500, overdraft = 10 ) > romain$balance
- 25. Questions ? Romain François http://romainfrancois.blog.free.fr romain@r-enthusiasts.com Chicago Local R User Group, Oct 27th , Chicago.