ALTREP error with `unique()`

[mllg]

Minimal reproducible example

x = as.data.table(iris)
x[["foo"]] = 1:150
unique(x, by = "Species")

This yields:

Internal error in subset.c: column 6 is an ALTREP vector. Please see NEWS item 2 in v1.11.4 and report this as a bug.

Tested with v11.4 and latest dev version.

Output of sessionInfo()

R version 3.5.1 (2018-07-02)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS High Sierra 10.13.6

Matrix products: default
BLAS: /Library/Frameworks/R.framework/Versions/3.5/Resources/lib/libRblas.0.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.5/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/de_DE.UTF-8/en_US.UTF-8/C/en_US.UTF-8/de_DE.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] nvimcom_0.9-75    gtfo_0.0.0.9000   devtools_1.13.6   data.table_1.11.5

loaded via a namespace (and not attached):
[1] compiler_3.5.1 tools_3.5.1    parallel_3.5.1 withr_2.1.2    memoise_1.1.0  digest_0.6.17 

[DavidArenburg]

That an awkward one, but as temporary fix, I would use the idiomatic data.table syntax which doesn't produce an error, e.g. x[, foo := 1:150] ; unique(x, by = "Species")

[petersteiner]

I have found a simple fix for all of these "ALTREP error" issues. You can do the following:
x <- copy(x) and unique(x, by="Species") will work.

[MichaelChirico]

@petersteiner that may work in a bind but it's not really recommended. What if you have a 15Gb data set and only 20Gb RAM?