Bug with Union type in Query.jl?

Specific Domains Data
1

I’d appreciate help to understand the following. The particular code here with a problem is using a @select expression to extract the second number embedded in a string in DataFrame column elements which have the type of Union{String, Missing}, but I expect the difficulty will probably arise with other variations (eg. I can confirm this fails with @where statements of similar form):

c1=Union{String, Missing}["a4 - 1.0","b5 - 2.0","c6 - 3.0"]

df2 = DataFrame(Frame=c1)

# Gives error (see below)
df3 = @from i in df2 begin
      @select {time=parse(Float64,string(match(r"[^\d]*[\d.]+[^\d]+([\d.]+)",i.Frame)[1])) }  # This is an error
      @collect DataFrame
end

# Good if I add extra string() conversion
df4 = @from i in df2 begin
      @select {time=parse(Float64,string(match(r"[^\d]*[\d.]+[^\d]+([\d.]+)",string(i.Frame))[1])) }
      @collect DataFrame
end

However the @select transformation expression above that gives an error works fine in “regular” Julia use

println("Extract 2nd digit: $(parse(Float64,string(match(r"[^\d]*[\d.]+[^\d]+([\d.]+)",c1[1])[1] ))))")

Is this a bug?

Many thanks,
GC

PS. The error thrown is:

LoadError: ArgumentError: unable to construct DataFrame from QueryOperators.EnumerableMap{Union{},QueryOperators.EnumerableIterable{NamedTuple{(:Frame, :Step),Tuple{DataValues.DataValue{String},DataValues.DataValue{String}}},Tables.DataValueRowIterator{NamedTuple{(:Frame, :Step),Tuple{DataValues.DataValue{String},DataValues.DataValue{String}}},Tables.RowIterator{NamedTuple{(:Frame, :Step),Tuple{Array{Union{Missing, String},1},Array{Union{Missing, String},1}}}}}},getfield(Main, Symbol("##269#270"))}
in expression starting at C:\Users\tcd\Dropbox (Personal)\Prof\TCD\Comm\Manuscript-19\Glass mech\Thin film yield\Analysis\queryPlay2.jl:32
#DataFrame#366(::Bool, ::Type, ::QueryOperators.EnumerableMap{Union{},QueryOperators.EnumerableIterable{NamedTuple{(:Frame, :Step),Tuple{DataValues.DataValue{String},DataValues.DataValue{String}}},Tables.DataValueRowIterator{NamedTuple{(:Frame, :Step),Tuple{DataValues.DataValue{String},DataValues.DataValue{String}}},Tables.RowIterator{NamedTuple{(:Frame, :Step),Tuple{Array{Union{Missing, String},1},Array{Union{Missing, String},1}}}}}},getfield(Main, Symbol("##269#270"))}) at tables.jl:35
DataFrame(::QueryOperators.EnumerableMap{Union{},QueryOperators.EnumerableIterable{NamedTuple{(:Frame, :Step),Tuple{DataValues.DataValue{String},DataValues.DataValue{String}}},Tables.DataValueRowIterator{NamedTuple{(:Frame, :Step),Tuple{DataValues.DataValue{String},DataValues.DataValue{String}}},Tables.RowIterator{NamedTuple{(:Frame, :Step),Tuple{Array{Union{Missing, String},1},Array{Union{Missing, String},1}}}}}},getfield(Main, Symbol("##269#270"))}) at tables.jl:20
top-level scope at none:0
2

I think this is about missing values are represented with DataValue in Query.jl. You may unpack DataValue to access stored variable via get(x) or x[]. The following should work.

df3 = @from i in df2 begin
             @select {time=parse(Float64, match(r"[^\d]*[\d.]+[^\d]+([\d.]+)", i.Frame[])[1]) }
             @collect DataFrame
       end
3

Thanks @hckr, that worked and is right in the docs, which I somehow didn’t catch.