Include only required fields in data

src/rendering/render.jl

@@ -202,11 +202,15 @@ end
 
 function Base.display(d::REPL.REPLDisplay, plt::VLSpec{:plot})
   # checkplot(plt)
-  tmppath = writehtml_full(JSON.json(getparams(plt)))
+  tmppath = writehtml_full(render_json(plt))
   launch_browser(tmppath) # Open the browser
 end
 
 function Base.display(d::REPL.REPLDisplay, plt::VGSpec)
   tmppath = write_vg_html_full(JSON.json(getparams(plt)))
   launch_browser(tmppath) # Open the browser
 end
+
+render_json(x) = sprint(render_json, x)
+render_json(io::IO, plt::VLSpec) =
+    JSON.print(io, getparams(with_stripped_data(plt)))

src/rendering/show.jl

@@ -21,7 +21,7 @@ end
 
 function convert_vl_to_vg(v::VLSpec{:plot})
     vl2vg_script_path = joinpath(@__DIR__, "vl2vg.js")
-    data = JSON.json(getparams(v))
+    data = render_json(v)
     p = open(`$(nodejs_cmd()) $vl2vg_script_path`, "r+")
     writer = @async begin
         write(p, data)
@@ -39,7 +39,7 @@ end
 function convert_vl_to_x(v::VLSpec{:plot}, second_script)
     vl2vg_script_path = joinpath(@__DIR__, "vl2vg.js")
     full_second_script_path = joinpath(@__DIR__, "..", "..", "deps", "node_modules", "vega-cli", "bin", second_script)
-    data = JSON.json(getparams(v))
+    data = render_json(v)
     p = open(pipeline(`$(nodejs_cmd()) $vl2vg_script_path`, `$(nodejs_cmd()) $full_second_script_path`), "r+")
     writer = @async begin
         write(p, data)
@@ -75,7 +75,7 @@ Base.Multimedia.istextmime(::MIME{Symbol("application/vnd.vegalite.v3+json")}) =
 Base.Multimedia.istextmime(::MIME{Symbol("application/vnd.vega.v5+json")}) = true
 
 function Base.show(io::IO, m::MIME"application/vnd.vegalite.v3+json", v::VLSpec{:plot})
-     print(io, JSON.json(getparams(v)))
+    render_json(io, v)
 end
 
 function Base.show(io::IO, m::MIME"application/vnd.vega.v5+json", v::VGSpec)

src/vlspec.jl

@@ -90,3 +90,32 @@ end
 Create a copy of `spec` without data.  See also [`deletedata!`](@ref).
 """
 deletedata(spec::VLSpec) = deletedata!(copy(spec))
+
+push_field!(fields, _) = fields
+push_field!(fields, xs::AbstractVector) = foldl(push_field!, xs; init=fields)
+function push_field!(fields, dict::AbstractDict)
+    f = get(dict, "field", nothing)
+    f !== nothing && push!(fields, string(f))
+    for v in values(dict)
+        push_field!(fields, v)
+    end
+    return fields
+end
+
+encoding_fields(spec::VLSpec) = encoding_fields(getparams(spec))
+function encoding_fields(specdict)
+    fields = Set{String}()
+    for (k, v) in specdict
+        k == "data" && continue
+        push_field!(fields, v)
+    end
+    return sort!(collect(fields))
+end
+
+function with_stripped_data(spec::VLSpec)
+    fields = encoding_fields(spec)
+    vals = get(get(getparams(spec), "data", Dict()), "values", nothing)
+    vals isa AbstractVector || return spec
+    vals = map(row -> Dict(f => get(row, f, nothing) for f in fields), vals)
+    return @set spec.data.values = vals
+end