I tried that, but I get an error:

```
No user recipe defined for Symbol
Stacktrace:
[1] copy!(::Array{Any,1}, ::Base.Generator{Array{Symbol,1},Plots.##223#225{Dict{Symbol,Any}}}) at ./abstractarray.jl:573
[2] convertToAnyVector(::Array{Symbol,1}, ::Dict{Symbol,Any}) at /home/rick/.julia/v0.6/Plots/src/series.jl:58
[3] macro expansion at /home/rick/.julia/v0.6/Plots/src/series.jl:131 [inlined]
[4] apply_recipe(::Dict{Symbol,Any}, ::Type{Plots.SliceIt}, ::Array{Symbol,1}, ::Array{Float64,1}, ::Void) at /home/rick/.julia/v0.6/RecipesBase/src/RecipesBase.jl:291
[5] _process_userrecipes(::Plots.Plot{Plots.GRBackend}, ::Dict{Symbol,Any}, ::Tuple{Array{Symbol,1},Array{Float64,1}}) at /home/rick/.julia/v0.6/Plots/src/pipeline.jl:81
[6] _plot!(::Plots.Plot{Plots.GRBackend}, ::Dict{Symbol,Any}, ::Tuple{Array{Symbol,1},Array{Float64,1}}) at /home/rick/.julia/v0.6/Plots/src/plot.jl:179
[7] #plot#212(::Array{Any,1}, ::Function, ::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/Plots/src/plot.jl:58
[8] (::RecipesBase.#kw##plot)(::Array{Any,1}, ::RecipesBase.#plot, ::Array{Symbol,1}, ::Array{Float64,1}, ::Vararg{Array{Float64,1},N} where N) at ./<missing>:0
[9] #violin#766(::Array{Any,1}, ::Function, ::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/RecipesBase/src/RecipesBase.jl:385
[10] violin(::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/RecipesBase/src/RecipesBase.jl:385
[11] #add_label#15(::Array{Any,1}, ::Function, ::Array{String,1}, ::Function, ::Array{Symbol,1}, ::Vararg{Any,N} where N) at /home/rick/.julia/v0.6/StatPlots/src/df.jl:129
[12] (::##75#76)(::DataFrames.DataFrame) at ./<missing>:0
[13] |>(::DataFrames.DataFrame, ::##75#76) at ./operators.jl:862
[14] include_string(::String, ::String) at ./loading.jl:522
```