CODEWITHSUNDEEP
rdata.tablereference-class
mchen
mchen

Reputation: 10156

How to extend a data.table using Reference Classes?

Problem:

I wish to create a Reference Class that extends a data.table.

The motivation being

  1. Want a data.table with custom methods and mutable fields
  2. Still want all existing syntax (such as indexing, subset, merge etc) to work as expected

Problem is I have so far failed.

Attempts:

I tried:

MyDataTable <- setRefClass("MyDataTable",
    methods = list(
        clearCell = function(i, j) {        # A trivial custom method - sets a cell to NA
            .self[i, (j) := NA]
        }
    ),
    contains = "data.table"
)

MyDataTable(a = 1:26, b = letters)$clearCell(1, 1)

But got the error:

Error in envRefSetField(.Object, field, classDef, selfEnv, elements[[field]]) : 
  ‘a’ is not a field in class “MyDataTable”

However, I was expecting something like:

     a b
 1: NA a
 2:  2 b
 3:  3 c
 4:  4 d
 5:  5 e
 6:  ... etc etc

What's going wrong?

Upvotes: 2

Views: 505

Answers (1)

eddi
eddi

Reputation: 49448

You're not initializing your reference class object correctly. I don't know how contains is supposed to work, but a simple field works:

MyDataTable <- setRefClass("MyDataTable",
                   fields  = list(.dt = 'data.table'),
                   methods = list(initialize = function(...){
                                    .self$.dt <- data.table(...)
                                  },
                                  clearCell  = function(i, j){
                                    .self$.dt[i, (j) := NA]
                                  },
                                  bracket    = function(...){
                                    .self$.dt[...]
                                  }
                                  ))

MyDataTable(a = 1:5, b = letters[1:5])$clearCell(1,1)
#    a b
#1: NA a
#2:  2 b
#3:  3 c
#4:  4 d
#5:  5 e

MyDataTable(a = 1:5, b = letters[1:5])$bracket(b == 'c', a := 10)
#    a b
#1:  1 a
#2:  2 b
#3: 10 c
#4:  4 d
#5:  5 e

Upvotes: 1

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