R help - Jan 2018 - Help with first S3-class

On 3 January 2018 at 00:52, Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:
> On 02/01/2018 6:38 PM, Martin M?ller 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.
Here is my second attempt making a S3-class.
But something is wrong with the deposit.account() ? Thanks for any help.

I expect this output:

[1] 0
Martin
Saldo is:  100

but I get this:

[1] 100
Martin
Saldo is:  0

Regards
Martin

account <- function(owner = NULL) {
if (is.null(owner)) stop("Owner can't be NULL")
value <- list(owner = owner, saldo = 0)
attr(value, "class") <- "account"
value
}

balance <- function(obj) { UseMethod("balance") }

balance.account <- function(obj) {
obj$saldo
}

deposit <- function(obj, amount) { UseMethod("deposit") }

deposit.account <- function(obj, amount) {
obj$saldo <- obj$saldo + amount
}

print.account <- function(obj) {
cat(obj$owner, "\n")
cat("Saldo is: ", obj$saldo, "\n")
}

A1 <- account("Martin")
deposit(A1, 100)
balance(A1)
print(A1)

Some mistake:
> I expect this output:
[1] 100
Martin
Saldo is: 100

but I get

[1] 0
Martn
Saldo is: 0

Function arguments are not pass-by-reference... they are pass-by-value. You need
to return the altered object to the caller when you are done messing with it.

Note that R is a data processing language... your example will not scale to real
world use cases because you make no use of vectorization to handle multiple
accounts. It is better to focus on the functional aspect of computing and let
the objects carry the results until you have a chance to summarize or plot them.
Study the "lm" function and associated print and plot methods.
-- 
Sent from my phone. Please excuse my brevity.

On January 2, 2018 4:37:01 PM PST, "Martin M?ller Skarbiniks Pedersen"
<traxplayer at gmail.com> wrote:
>Some mistake:
>
>> I expect this output:
>
>[1] 100
>Martin
>Saldo is: 100
>
>but I get
>
>[1] 0
>Martn
>Saldo is: 0
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.