copy does not copy to standard Julia Types

[schlichtanders]

While the documentation says that a copy would ensure to have normal Julia Types

df = copy(DataFrame(Arrow.Table(file))): Build a DataFrame, where the columns are regular in-memory vectors (specifically, Base.Vectors and/or PooledVectors). This requires that you have enough memory to load the entire DataFrame into memory.

this is not the case

[Moelf]

maybe that's because result_old[!, "workers"] is not a ::DataFrame?

[schlichtanders]

Interesting, could be, but then, why are only DataFrames supported for copy and not regular Arrays?

[Moelf]

Because you extracted just a column, which is not a data frame, so copy specialized for data frame doesn't work

[ericphanson]

I think the other answer is because (if I understand correctly) it's a DataFrames.jl feature, not an Arrow.jl feature, it's just documented here because it's a common ask

[ericphanson]

Maybe collect is what's desired here, for materializing a column into a Vector? Naively collect should be "iterate this collection into an Array", though I haven't tried it in this case