In R, how can I check if two variable names reference the same underlying object?

Question

For example:

A <- 1:10
B <- A

Both A and B reference the same underlying vector.

Before I plow off and implement something in

Answer 1

I found this question when looking for a function that checks whether a single variable is referenced at all, especially in the context of data.table. Extending the other answers, I believe the following function does this:

is_referenced <- function(x) {
  nom <- as.character(substitute(x))
  ls_ <- ls(parent.frame())
  ls_ <- ls_[ls_ != nom]
  tr <- tracemem(x)
  for (i in ls_) {
    if (identical(x, get(i, envir = parent.frame()))) {
      if (identical(tr, tracemem(get(i, envir = parent.frame())))) {
        untracemem(x)
        untracemem(get(i, envir = parent.frame()))
        print(i)
        return(TRUE)
      } else {
        untracemem(get(i, envir = parent.frame()))
      }
    }
  }
  untracemem(x)
  FALSE
} 

x <- 1:10
y <- x
is_referenced(x)
#> [1] "y"
#> [1] TRUE

z <- 1:10
is_referenced(z)
#> [1] FALSE

y[1] <- 1L
is_referenced(y)
#> [1] FALSE


library(data.table)
DT <- data.table(x = 1)
ET <- DT
is_referenced(DT)
#> [1] "ET"
#> [1] TRUE
is_referenced(ET)
#> [1] "DT"
#> [1] TRUE

ET[, y := 1]
is_referenced(DT)
#> [1] "ET"
#> [1] TRUE

DT <- copy(ET)
is_referenced(DT)
#> [1] FALSE

^{Created on 2018-08-07 by the reprex package (v0.2.0).}