setorder orders by reference!

gistfile1.txt

  library(data.table)
  
  dt <- data.table(a = 1:10, b = 20:11)
  dt
  setorder(dt, a)
  ord_a <- dt[["a"]]
  ord_a
  setorder(dt, b)
  ord_b <- dt[["b"]]
  ord_b
  # this seems all good, but now this happened:
  ord_a

  # doesn't happen here:
  dt <- data.table(a = 1:10, b = 20:11)
  dt
  dt[order(a),]
  ord_a <- dt[["a"]]
  ord_a
  dt[order(b),]
  ord_b <- dt[["b"]]
  ord_b
  ord_a
  
  # also doesn't happen here:
  dt <- data.table(a = 1:10, b = 20:11)
  dt
  setorder(dt, a)
  ord_a <- c(dt[["a"]])
  ord_a
  setorder(dt, b)
  ord_b <- c(dt[["b"]])
  ord_b
  ord_a