Violin plot (#25)

* begin work on violin plot

* testing

* Violin plots (draft)

* Better violin plots

* Better violin plots

* documentation and clean

* update test

* Add to manual and fix typo

* rename to `add-violin`

* document kernal signature

* update tests

manual.typ

@@ -54,7 +54,7 @@ module imported into the namespace.
 = Plot
 
 #doc-style.parse-show-module("/src/plot.typ")
-#for m in ("line", "bar", "boxwhisker", "contour", "errorbar", "annotation", "formats") {
+#for m in ("line", "bar", "boxwhisker", "contour", "errorbar", "annotation", "formats", "violin") {
   doc-style.parse-show-module("/src/plot/" + m + ".typ")
 }
 

src/plot.typ

@@ -12,6 +12,7 @@
 #import "/src/plot/bar.typ": add-bar
 #import "/src/plot/errorbar.typ": add-errorbar
 #import "/src/plot/mark.typ"
+#import "/src/plot/violin.typ": add-violin
 #import "/src/plot/formats.typ"
 #import plot-legend: add-legend
 

src/plot/violin.typ

@@ -0,0 +1,135 @@
+#import "/src/cetz.typ": draw
+#import "util.typ"
+#import "sample.typ"
+
+#let kernel-normal(x, stdev: 1.5) = {
+  (1/calc.sqrt(2*calc.pi*calc.pow(stdev,2))) * calc.exp( - (x*x)/(2*calc.pow(stdev,2)))
+}
+
+#let _violin-render(self, ctx, violin, filling: true) = {
+  let path = range(self.samples)
+              .map((t)=>violin.min + (violin.max - violin.min) * (t /self.samples ))
+              .map((u)=>(u, (violin.convolve)(u)))
+              .map(((u,v)) => {
+                (violin.x-position + v, u)
+              })
+
+  if self.side == "both"{ 
+    path += path.rev().map(((x,y))=> {(2 * violin.x-position - x,y)})
+  } else if self.side == "left"{
+    path = path.map( ((x,y))=>{(2 * violin.x-position - x,y)})
+  }
+
+  let (x, y) = (ctx.x, ctx.y)
+  let stroke-paths = util.compute-stroke-paths(path, (x.min, y.min), (x.max, y.max))
+
+  for p in stroke-paths{
+    let args = arguments(..p, closed: self.side == "both")
+    if filling {
+      args = arguments(..args, stroke: none)
+    } else {
+      args = arguments(..args, fill: none)
+    }
+    draw.line(..self.style, ..args)
+  }
+}
+
+#let _plot-prepare(self, ctx) = {
+  self.violins = self.data.map(entry=> {
+    let points = entry.at(self.y-key)
+    let (min, max) = (calc.min(..points), calc.max(..points))
+    let range = calc.abs(max - min)
+    (
+      x-position: entry.at(self.x-key),
+      points: points,
+      length: points.len(),
+      min: min - (self.extents * range),
+      max: max + (self.extents * range),
+      convolve: (t) => {
+        points.map((y)=>(self.kernel)((y - t)/self.bandwidth)).sum() / (points.len() * self.bandwidth)
+      }
+    )
+  })
+  return self
+}
+
+#let _plot-stroke(self, ctx) = { 
+  for violin in self.violins {
+    _violin-render(self, ctx, violin, filling: false)
+  }
+}
+
+#let _plot-fill(self, ctx) = { 
+  for violin in self.violins {
+    _violin-render(self, ctx, violin, filling: true)
+  }
+}
+
+#let _plot-legend-preview(self) = {
+  draw.rect((0,0), (1,1), ..self.style)
+}
+
+
+/// Add a violin plot
+///
+/// A violin plot is a chart that can be used to compare the distribution of continuous
+/// data between categories.
+///
+/// - data (array): Array of data items. An item is an array containing an `x` and one 
+///                 or more `y` values.
+/// - x-key (int, string): Key to use for retreiving the `x` position of the violin.
+/// - y-key (int, string): Key to use for retreiving values of points within the category.
+/// - side (string): The sides of the violin to be rendered:
+///   / left: Plot only the left side of the violin.
+///   / right: Plot only the right side of the violin.
+///   / both: Plot both sides of the violin.
+/// - kernel (function): The kernel density estimator function, which takes a single
+///                      `x` value relative to the center of a distribution (0) and
+///                      normalized by the bandwidth
+/// - bandwidth (float): The smoothing parameter of the kernel.
+/// - extents (float): The extension of the domain, expressed as a fraction of spread.
+/// - samples (int): The number of samples of the kernel to render.
+/// - style (dictionary): Style override dictionary.
+/// - mark-style (dictionary): (unused, will eventually be used to render interquartile ranges).
+/// - axes (axes): (unstable, documentation to follow once completed).
+/// - label (none, content): The name of the category to be shown in the legend.
+#let add-violin( 
+  data,
+  x-key: 0,
+  y-key: 1,
+  side: "right",
+  kernel: kernel-normal.with(stdev: 1.5),
+  bandwidth: 1,
+  extents: 0.25,
+
+  samples: 50,
+  style: (:),
+  mark-style: (:),
+  axes: ("x", "y"),
+  label: none,
+) = {
+
+  ((
+    type: "violins",
+
+    data: data,
+    x-key: x-key,
+    y-key: y-key,
+    side: side,
+    kernel: kernel,
+    bandwidth: bandwidth,
+    extents: extents,
+
+    samples: samples,
+    style: style,
+    mark-style: mark-style,
+    axes: axes,
+    label: label,
+
+    plot-prepare: _plot-prepare,
+    plot-stroke: _plot-stroke,
+    plot-fill: _plot-fill,
+    plot-legend-preview: _plot-legend-preview,
+  ),)
+
+}

tests/plot/violin/test.typ

@@ -0,0 +1,63 @@
+#set page(width: auto, height: auto)
+#import "/src/lib.typ": *
+#import "/src/cetz.typ": *
+#import "/tests/helper.typ": *
+
+/* Empty plot */
+#test-case({
+  import draw: *
+
+  draw.set-style(
+    axes: (
+      stroke: 0.55pt,
+      tick: (
+        stroke: 0.5pt,
+      )
+    ),
+    legend: (
+      stroke: none,
+    )
+  )
+
+  let default-colors = (palette.blue-colors.at(3), palette.pink-colors.at(3))
+
+  plot.plot(size: (9, 6),
+
+    y-label: [Age],
+    y-min: -10, y-max: 20,
+    y-tick-step: 10, y-minor-tick-step: 5,
+    y-grid: "major",
+
+    x-label: [Class],
+    x-min: -0.5, x-max: 2.5,
+    x-tick-step: none,
+    x-ticks: ( (0, [First]), (1, [Second]), (2, [Third])),
+
+    plot-style: (i) => {
+      let color = default-colors.at(calc.rem(i, default-colors.len()))
+      (stroke: color + 0.75pt, fill: color.lighten(75%))
+    },
+  {
+    let vals = (
+      (0,(5,4,6,8,5.1,4.1,1,5.2,5.3,5.4,4.2,2,5.5,4.3,6,5,4,5,8,4,5,)),
+      (1,(5,4,6,8,5.1,4.1,1,5.2,5.3,5.4,4.2,2,5.5,4.3,6,5,4,5,8,4,5,)),
+      (2,(5,4,6,8,5.1,4.1,1,5.2,5.3,5.4,4.2,2,5.5,4.3,6,5,4,5,8,4,5,)),
+    )
+
+    cetz-plot.plot.add-violin(
+      vals,
+      extents: 0.5,
+      side: "left",
+      bandwidth: 0.45,
+      label: [Male],
+    )
+
+    cetz-plot.plot.add-violin(
+      vals,
+      extents: 0.5,
+      side: "right",
+      bandwidth: 0.5,
+      label: [Female]
+    )
+  })
+})