[WIP] prelim version of the density geometry revamp

working on #1152.

Note: This is a WIP and currently completely breaks `Geom.density` and
`Geom.violin` has several regressions.

src/aesthetics.jl

@@ -1,3 +1,5 @@
+using IterTools
+
 const NumericalOrCategoricalAesthetic =
     Union{(Void), Vector, DataArray, IndirectArray}
 
@@ -413,3 +415,72 @@ function inherit!(a::Aesthetics, b::Aesthetics;
     end
     nothing
 end
+
+"""
+    Given aesthetics to group with, `by`, and an aesthetic to group `togroupvar`
+this function constructs a dictionary that maps each given combination of the
+`by` aesthetics to the positions which they apply to. Thus the output is a
+dictionary of tuples of each unique combination of `by` mapped to a boolean
+array of length `n` where `n` is the length of the aesthetics (they have to all
+have the same length). If the provided aesthetics are missing, a placeholder
+`nothing` is return instead of the unique value.
+
+## Examples
+
+```jldoctest
+aes = Gadfly.Aesthetics()
+aes.x = repeat([1, 2], inner=3)
+aes.y = collect(1:6)
+
+groupby(aes, [:x, :color], :y)
+
+# output
+
+Dict((2, nothing)=>Bool[false, false, false, true, true, true],(1, nothing)=>Bool[true, true, true, false, false, false])
+```
+
+```jldoctest
+aes = Gadfly.Aesthetics()
+aes.x = repeat([:a, :b], inner=2)
+aes.y = collect(1:4)
+aes.color = repeat([colorant"red", colorant"blue"], inner=2)
+
+groupby(aes, [:x, :color], :y)
+
+# output
+
+Dict((:a, RGB{N0f8}(1.0,0.0,0.0))=>Bool[true, true, false, false],(:b, RGB{N0f8}(0.0,0.0,1.0))=>Bool[false, false, true, true])
+```
+
+"""
+function groupby(aes::Gadfly.Aesthetics, by::Vector{Symbol}, togroupvar::Symbol)
+    types = fill(Nothing, length(by))
+    isconcrete = fill(false, length(by))
+    for i in 1:length(by)
+        isconcrete[i] = getfield(aes, by[i]) != nothing
+        (!isconcrete[i]) && continue
+        types[i] = eltype(getfield(aes, by[i]))
+        @assert length(getfield(aes, togroupvar)) == length(getfield(aes, by[i])) "$togroupvar and $(by[i]) aesthetics must have same length"
+    end
+
+    T = Tuple{types...}
+    grouped = Dict{T, Vector{Bool}}()
+
+    # gather options for each `by` aesthetic
+    opt = [if isconcrete[i] unique(getfield(aes, by[i])) else [nothing] end for i in 1:length(by)]
+
+    # The approach is to identify positions were multiple by aesthetics overlap
+    # and thus grouping the data positions. We first assume that all positions
+    # belong to a combination of aesthetics and then whittle it down
+    for combo in product(opt...)
+        belongs = fill(true, length(getfield(aes, togroupvar)))
+        for i in 1:length(combo)
+            (combo[i] == nothing) && continue
+            belongs .&= getfield(aes, by[i]) .== combo[i]
+        end
+        # for multiple by variables we need to check whether there is any overlap
+        # between this specific combo before adding it to the dict
+        (any(belongs)) && (grouped[combo] = belongs)
+    end
+    grouped
+end

src/geom/density.jl

@@ -1,8 +1,29 @@
+struct DensityGeometry <: Gadfly.GeometryElement
+    stat::Gadfly.StatisticElement
+    order::Int
+    tag::Symbol
+end
+
+function DensityGeometry(; order=1, tag=empty_tag, kwargs...)
+    DensityGeometry(Gadfly.Stat.DensityStatistic(; kwargs...), order, tag)
+end
+
+DensityGeometry(stat; order=1, tag=empty_tag) = DensityGeometry(stat, order, tag)
+
+const density = DensityGeometry
+
+element_aesthetics(::DensityGeometry) = Symbol[]
+default_statistic(geom::DensityGeometry) = Gadfly.Stat.DensityStatistic(geom.stat)
+
 struct ViolinGeometry <: Gadfly.GeometryElement
+    stat::Gadfly.StatisticElement
+    split::Bool
     order::Int
     tag::Symbol
 end
-ViolinGeometry(; order=1, tag=empty_tag) = ViolinGeometry(order, tag)
+function ViolinGeometry(; order=1, tag=empty_tag, split=false, kwargs...)
+    ViolinGeometry(Gadfly.Stat.DensityStatistic(; kwargs...), split, order, tag)
+end
 
 """
     Geom.violin[(; order=1)]
@@ -15,29 +36,42 @@ const violin = ViolinGeometry
 
 element_aesthetics(::ViolinGeometry) = [:x, :y, :color]
 
-default_statistic(::ViolinGeometry) = Gadfly.Stat.violin()
+default_statistic(geom::ViolinGeometry) = Gadfly.Stat.DensityStatistic(geom.stat)
 
 function render(geom::ViolinGeometry, theme::Gadfly.Theme, aes::Gadfly.Aesthetics)
-    # TODO: What should we do with the color aesthetic?
 
     Gadfly.assert_aesthetics_defined("Geom.violin", aes, :y, :width)
     Gadfly.assert_aesthetics_equal_length("Geom.violin", aes, :y, :width)
 
-    default_aes = Gadfly.Aesthetics()
-    default_aes.color = fill(theme.default_color, length(aes.y))
-    aes = Gadfly.inherit(aes, default_aes)
-
-    # Group y, width and color by x
-    ux = unique(aes.x)
-    grouped_color = Dict(x => first(aes.color[aes.x.==x]) for x in ux)
-    grouped_y = Dict(x => aes.y[aes.x.==x] for x in ux)
-    grouped_width = Dict(x => aes.width[aes.x.==x] for x in ux)
-
-    kgy = keys(grouped_y)
-    violins = [vcat([(x - w/2, y) for (y, w) in zip(grouped_y[x], grouped_width[x])],
-                reverse!([(x + w/2, y) for (y, w) in zip(grouped_y[x], grouped_width[x])]))
-                for x in kgy]
-    colors = [grouped_color[x] for x in kgy]
+    grouped_data = Gadfly.groupby(aes, [:x, :color], :y)
+    violins = Array{NTuple{2, Float64}}[]
+
+    colors = []
+    (aes.color == nothing) && (aes.color = fill(theme.default_color, length(aes.x)))
+    color_opts = unique(aes.color)
+    if geom.split && length(color_opts) > 2
+        error("Split violins require 2 colors, not more")
+    end
+
+    for (keys, belongs) in grouped_data
+        x, color = keys
+        ys = aes.y[belongs]
+        ws = aes.width[belongs]
+
+        if geom.split
+            pos = findfirst(color_opts, color)
+            if pos == 1
+                push!(violins, [(x - w/2, y) for (y, w) in zip(ys, ws)])
+            else
+                push!(violins, reverse!([(x + w/2, y) for (y, w) in zip(ys, ws)]))
+            end
+            push!(colors, color)
+        else
+            push!(violins, vcat([(x - w/2, y) for (y, w) in zip(ys, ws)],
+                                reverse!([(x + w/2, y) for (y, w) in zip(ys, ws)])))
+            push!(colors, color != nothing ? color : theme.default_color)
+        end
+    end
 
     ctx = context(order=geom.order)
     compose!(ctx, Compose.polygon(violins, geom.tag), fill(colors))

src/geom/line.jl

@@ -51,16 +51,6 @@ geometry is equivalent to [`Geom.line`](@ref) with `preserve_order=true`.
 """
 path() = LineGeometry(preserve_order=true)
 
-"""
-    Geom.density[(; bandwidth=-Inf)]
-
-Draw a line showing the density estimate of the `x` aesthetic.
-This geometry is equivalent to [`Geom.line`](@ref) with
-[`Stat.density`](@ref); see the latter for more information.
-"""
-density(; bandwidth::Real=-Inf) =
-    LineGeometry(Gadfly.Stat.density(bandwidth=bandwidth))
-
 """
     Geom.density2d[(; bandwidth=(-Inf,-Inf), levels=15)]