[datatable-help] Access to local variables in "j" expressions

[Johann Hibschman]

I'm just taking a look at data.table again, now that 1.4.1 has been
released. I tried the following:

  dt.test <- data.table(n=c("a","a","b"), x=1:3, key="n")

  global.sum7 <- function (y) {
   sum(y) + 7
  }

  test.1 <- function (dt) {
   local.sum7 <- global.sum7
   dt[, list(out=local.sum7(x)), by=n]
  }

  test.1(dt.test)

 This failed, with 'Error in eval(expr, envir, enclos) : could not
find function "local.sum7"'. Looking at the documentation, I see:

     The j expression 'sees' variables in the calling frame and above
     including .GlobalEnv, see the examples. This is base R
     functionality from eval() and with().

That led me to think that the above would work. Is this a bug, or am I
not understanding something?

Thanks,
Johann