Loading R6 objects that have data.table fields

Question

This is very closely related to: Adding new columns to a data.table by-reference within a function not always working

How do you make setalloccol work on data tables (data.table_1.16.0) that are a field of a R6 object loaded from disk. For example, following closely the code from the linked post:

library(R6)
library(data.table)
testR6 <- R6Class("testR6", 
                   public = list(initialize = function(test_) {
                       self$test <- test_
                   }),
                   private = list(.test = data.table()),
                   active = list(test = function(val) if (missing(val)) private$.test else private$.test <- val
                                 )
)


foobar <- function(dt, col) {
    dt[, (col) := 1]
    invisible(dt)
}


test <- data.table(id = letters[1:2], val=1:2)
test_R6 <- testR6$new(test)
saveRDS(test_R6, "data_20251008_test_R6.rds")
test_R6_2 <- readRDS("data_20251008_test_R6.rds")

all.equal(test_R6, test_R6_2)
#[1] TRUE
truelength(test_R6$test)
# [1] 1026
truelength(test_R6_2$test)
# [1] 0

setalloccol(test_R6_2$test)
truelength(test_R6_2$test)
# [1] 0 ## DID NOT WORK!




foobar(test_R6$test, "new")
test_R6$test
#  id val new
#1: a   1   1
#2: b   2   1
foobar(test_R6_2$test, "new")
test_R6_2$test
# id   val
# <char> <int>
#     1:      a     1
# 2:      b     2

It is possible to use setDT on this simple data.table, and the subsequent call to foobar works, i.e.:

test_R6_3 <- readRDS("data_20251008_test_R6.rds")
setDT(test_R6_3$test)
truelength(test_R6_3$test)
# [1] 1026

This workaround doesn't work for my very complicated dataset (which I cannot easily reproduce here). I obtain a different type of error when I call setDT:

Error in stop() : argument "..1" is missing, with no default

Grasshopper_NZ · Accepted Answer · 2025-10-08 06:57:42Z

0

Add:

test_R6_2$test <- as.data.table(test_R6_2$test)

Then test_R6_2 will yield the same result:

foobar(test_R6$test, "new")

test_R6$test
       id   val   new
   <char> <int> <num>
1:      a     1     1
2:      b     2     1

foobar(test_R6_2$test, "new")

test_R6_2$test
       id   val   new
   <char> <int> <num>
1:      a     1     1
2:      b     2     1

answered Oct 8 at 6:57

Grasshopper_NZ

1,0627 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Alex Oct 8 at 9:40

This copies the object in memory though?

Collectives™ on Stack Overflow

Loading R6 objects that have data.table fields

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related