Implementing Tables interface for types with optional missing/nothing

[xvries]

Hey all,

I would like to implement the Tables interface for my custom types. We have a lot of types which have optional fields: Sometimes they have a value and sometimes they report a nothing or a missing. I guess I could get it to work by custom defining every struct with optional fields, but is there a more simple way. Here is a simple example:

struct MyType
	i::Int64
	f::Float64
	o::Union{Nothing, String}
end
Tables.istable(::Type{MyType}) = true
Tables.columnaccess(::Type{MyType}) = true
Tables.columns(m::MyType) = m

m = MyType(1, 0.3, nothing)
DataFrame(m)

This does not work because length(::Nothing) is not defined. Is there a general way to fix this?

[quinnj]

Hmmm, is MyType really a "column table" though? It seems more like one instance of a MyType object is more like a single row in a row-oriented table? Individual columns in column-tables should be some kind of AbstractVector.

[xvries]

Indeed if its one element its not really a column table, but if it is a Vector{MyType} then I want to be able to make a table out of it. Is that possible in some other way then?