[R] R6 object that is a list of referenced object

[Eric Berger]

Hi Cristina,
You can try this:

> Community <- R6Class("Community",
                       public = list(
                         e = NULL,
                         initialize = function() { self$e <- list() },
                         add = function( person ) { self$e[[ length(self$e)
+ 1]] <<- person }
                       )
  )

> crowd <- Community$new()
> crowd$add(Person1)
> crowd$add(Person2)
> crowd$e

HTH,
Eric


On Thu, Nov 16, 2017 at 9:55 AM, Jeff Newmiller <jdnewmil at dcn.davis.ca.us>
wrote:

> See below.
>
> On Wed, 15 Nov 2017, Cristina Pascual wrote:
>
> Dear community,
>>
>> I am having a class, let's say Person,
>>
>> Person <-  R6Class("Person",
>>                     public = list(
>>                       idPerson = NULL,
>>                       name = NULL,
>>                       age = NULL,
>>                       initialize = function(idPerson = NA, name = NA, age
>> = NA) {
>>
>
> It is a bad idea to setup default values for all your parameters in any
> function, but particularly so for an initialization function. A Person with
> NA in the idPerson field is essentially unusable, so encouraging the
> creation of such an object is very bad practice.
>
>                        self$idPerson <- idPerson
>>                        self$name <- name
>>                        self$age <- age
>>                       }
>>                     ) # public
>>
>> ) # Person
>>
>> I have created:
>> Person1 <- Person$new(1,'a',4)
>> Person2 <- Person$new(2,'b',5)
>>
>> and I also have a class Community:
>>
>> Community <- R6Class("Community",
>>                 public = list(
>>                   e = NULL,
>>                   initialize = function() self$e <- Person$new()
>>
>
> Initializing a Community with a bogus person is as bad as the idPerson
> being NA. It makes a lot more sense to have the set of persons in a
> community be the null set than to have a minimum of one person in the
> community who happens to have invalid identification.
>
>                 )
>> )
>>
>> I want to create
>>
>> Community1 = List<Person>
>>
>> and add Person1 and Person2 to Community1 (Community1 <-
>> Community1$add(Person1)
>>
>>          Community1 <- Community1$add(Person2)
>>
>> ????)
>>
>> How can I write this with R6? I cannot find the proper example in the
>> website.
>>
>> Can anybody help me?
>>
>> Thanks in advance,
>>
>
> You don't seem to be very familiar with either R or conventional
> object-oriented design. Although I am giving you a reprex below, I
> recommend that you avoid R6 until you are more familiar with how normal
> functional programming and S3 object oriented coding styles work in R.
> Using R6 as a crutch to avoid that learning process will only lead you to
> frustration and inefficient data handling. That is, this whole thing should
> just be a data frame.
>
> ########################################
> library(R6)
> Person <-  R6Class( "Person"
>                   , public = list( idPerson = NA
>                                  , name = NA
>                                  , age = NA
>                                  , initialize = function( idPerson
>
>                      , name
>
>                      , age
>
>                      ) {
>
>                self$idPerson <- idPerson
>
>                self$name <- name
>
>                self$age <- age
>
>              }
>                      ) # public
>                   ) # Person
>
> Person1 <- Person$new( 1, 'a', 4 )
> Person2 <- Person$new( 2, 'b', 5 )
>
> Community <- R6Class( "Community"
>                     , public = list( e = NULL
>
> , addPerson = function( p ) {
>
>    self$e <- append( self$e, p )
>
>   }
>
> )
>                     )
>
> Community1 <- Community$new()
> Community1$addPerson( Person1 )
> Community1$addPerson( Person2 )
> Community1$e
> #> [[1]]
> #> <Person>
> #>   Public:
> #>     age: 4
> #>     clone: function (deep = FALSE)
> #>     idPerson: 1
> #>     initialize: function (idPerson, name, age)
> #>     name: a
> #>
> #> [[2]]
> #> <Person>
> #>   Public:
> #>     age: 5
> #>     clone: function (deep = FALSE)
> #>     idPerson: 2
> #>     initialize: function (idPerson, name, age)
> #>     name: b
>
> # Standard R approach:
> Person1a <- data.frame( idPerson = 1
>                       , name = "a"
>                       , age = 4
>                       , stringsAsFactors = FALSE
>                       )
> Person2a <- data.frame( idPerson = 2
>                       , name = "b"
>                       , age = 5
>                       , stringsAsFactors = FALSE
>                       )
> Community1a <- rbind( Person1a, Person2a )
> Community1a
> #>   idPerson name age
> #> 1        1    a   4
> #> 2        2    b   5
> ########################################
>
>
>>
>>
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>>
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>>
> ------------------------------------------------------------
> ---------------
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> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
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> ng-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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