Assigning attribute of environment object from within function by reference

Question

Here is a simplified example:

e <- new.env()
e$var <- 'some.val'
attr(e$var, 'attrib') <- 'some.attrib' 
attr(e$var, 'attrib')
#[1] "some.attrib"

assign_new_attrib <- function(obj) {
   attr(obj, 'attrib') <<- 'some.new.attrib'
}

assign_new_attrib(e$var)
#Error in attr(obj, "attrib") <<- "some.new.attrib" : 
#  object 'obj' not found
attr(e$var, 'attrib')
#[1] "some.attrib"

I have a variable var in environment e which has an attribute attrib. Now I have a function assign_new_attrib which takes a object and assigns it a new attribute attrib. As you can see, the above code results in a error "object 'obj' not found" due to the fact that <<- can not resolve the variable from within the function.

How can I define function assign_new_attrib() to assign the new attribute by referece?

If its not clear: the final result of attr(e$var, 'attrib') should be 'some.new.attrib'. — Davor Josipovic
– Davor Josipovic, Commented Nov 24, 2017 at 17:09
See the setattr function from data.table, if you want to change attributes by reference. Try assign_new_attrib_DT <- function(obj) data.table::setattr(obj, 'attrib', 'some.new.attrib'). — nicola
– nicola, Commented Nov 24, 2017 at 17:18
@nicola, that is a good answer. Don't know why you put it as a comment. I would definitely accept it! data.table is a very common package, and data.table::setattr() works on any object. — Davor Josipovic
– Davor Josipovic, Commented Nov 24, 2017 at 17:24

zx8754 · Accepted Answer · 2018-09-06 08:23:29Z

1

From the comments by nicola:

See the setattr function from data.table, if you want to change attributes by reference. Try:

assign_new_attrib_DT <- function(obj) data.table::setattr(obj, 'attrib', 'some.new.attrib')

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