On 02/01/2018 6:38 PM, Martin Møller Skarbiniks Pedersen wrote:
Hi,
I am trying to understand S3 classes. I have read several tutorials about
the topics but I am still a bit confused. I guess it is because it is
so different from
Java OOP.
What you do below isn't S3. S3 is a system where the classes are
secondary to the generic functions. Methods "belong" to generics, they
don't belong to classes. As far as I can see, you hardly make use of S3
methods and generics at all.
For the style you're using, the R6 or R.oo packages might be more suitable.
I have pasted my attempt at creating a bank-account class below and
my problems are:
1. What should be added some plot.default() calls the account$plot() method ?
No, you need to define a function called "plot.account" whose signature
is compatible with plot, i.e. arguments (x, y, ...), possibly with extra
parameters as well. It should do the plotting.
2. What should the account$plot() be implemented to show some kind of plot ?
The plot.account function could call account$plot(); it can do whatever
you want to plot the object.
3. How can one function inside "me"-list called another function. Eg.
How can account$plot() call account$pastSaldo() ?
There's no particular support for having them see each other the way
you've defined them. A better way to define them would be as local
functions within the account body; then they'd be able to see each other
without any prefix.
Duncan Murdoch
Here are my code. Feel free to comment on any aspect of the code.
ps. I hope I have manage to strip HTML.
Regards
Martin
account <- function(owner = NULL) {
thisEnv <- environment()
pastSaldo <- vector()
saldo <- 0
owner <- owner
me <- list(
thisEnv = thisEnv,
getEnv = function() { return(get("thisEnv", thisEnv)) },
balance = function() { return(get("saldo", thisEnv)) },
deposit = function(value) {
assign("pastSaldo", append(pastSaldo, saldo), thisEnv)
assign("saldo", saldo + value, thisEnv)
},
withdraw = function(value) {
assign("pastSaldo", append(pastSaldo, saldo), thisEnv)
assign("saldo", saldo - value, thisEnv)
},
pastSaldo = function() {
return(pastSaldo)
},
plot = function() {
plot.new()
lines(list(y = pastSaldo, x = seq_along(pastSaldo)))
}
)
assign('this', me, envir = thisEnv)
class(me) <- append(class(me), "account")
return(me)
}
FirstAccount <- account("Martin")
FirstAccount$deposit(100)
FirstAccount$withdraw(50)
FirstAccount$deposit(200)
FirstAccount$balance()
FirstAccount$pastSaldo()
FirstAccount$plot()
plot(FirstAccount) # fails
plot.account(FirstAccount) # fails
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