feat: add Violin trace type

Add the `Violin` trace with the full plotly.js violin attribute surface:
bandwidth, box (inner mini box plot), meanline, KDE span/spanmode,
scalegroup/scalemode, side (split violins), points/jitter/pointpos,
selected/unselected, quartilemethod, hoveron, and zorder.

Grouped and split violins work via the existing `ViolinMode` layout
attribute. Includes unit tests, a doctest, a statistical-charts example
(basic, horizontal, split), and a book recipe.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jqnatividad

CHANGELOG.md

@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ### Added
 
+- Add `Violin` trace type with box, mean line, KDE span, and split/grouped support
 - [[#406](https://github.com/plotly/plotly.rs/issues/406)] Expose `plotly.js` 3.1–3.6 attributes
 
 ### Changed

docs/book/src/SUMMARY.md

@@ -21,6 +21,7 @@
     - [Statistical Charts](./recipes/statistical_charts.md)
         - [Error Bars](./recipes/statistical_charts/error_bars.md)
         - [Box Plots](./recipes/statistical_charts/box_plots.md)
+        - [Violin Plots](./recipes/statistical_charts/violin_plots.md)
         - [Histograms](./recipes/statistical_charts/histograms.md)
     - [Scientific Charts](./recipes/scientific_charts.md)
        - [Contour Plots](./recipes/scientific_charts/contour_plots.md)

docs/book/src/recipes/statistical_charts.md

@@ -6,4 +6,5 @@ Kind | Link
 :---|:----:
 Error Bars |[![Scatter Plots](./img/error_bars.png)](./statistical_charts/error_bars.md)
 Box Plots | [![Line Charts](./img/box_plot.png)](./statistical_charts/box_plots.md)
+Violin Plots | [![Violin Plots](./img/box_plot.png)](./statistical_charts/violin_plots.md)
 Histograms | [![Scatter Plots](./img/overlaid_histogram.png)](./statistical_charts/histograms.md)

docs/book/src/recipes/statistical_charts/violin_plots.md

@@ -0,0 +1,36 @@
+# Violin Plots
+
+The following imports have been used to produce the plots below:
+
+```rust,no_run
+use plotly::common::{Line, Orientation};
+use plotly::layout::{Layout, ViolinMode};
+use plotly::violin::{MeanLine, ViolinBox, ViolinPoints, ViolinSide};
+use plotly::{color::NamedColor, Plot, Violin};
+```
+
+The `to_inline_html` method is used to produce the html plot displayed in this page.
+
+
+## Basic Violin Plot
+```rust,no_run
+{{#include ../../../../../examples/statistical_charts/src/main.rs:basic_violin_plot}}
+```
+
+{{#include ../../../../../examples/statistical_charts/output/inline_basic_violin_plot.html}}
+
+
+## Horizontal Violin Plot
+```rust,no_run
+{{#include ../../../../../examples/statistical_charts/src/main.rs:horizontal_violin_plot}}
+```
+
+{{#include ../../../../../examples/statistical_charts/output/inline_horizontal_violin_plot.html}}
+
+
+## Split Violin Plot
+```rust,no_run
+{{#include ../../../../../examples/statistical_charts/src/main.rs:split_violin_plot}}
+```
+
+{{#include ../../../../../examples/statistical_charts/output/inline_split_violin_plot.html}}

examples/statistical_charts/src/main.rs

@@ -6,8 +6,9 @@ use plotly::{
     color::{NamedColor, Rgb, Rgba},
     common::{ErrorData, ErrorType, Line, Marker, Mode, Orientation},
     histogram::{Bins, Cumulative, HistFunc, HistNorm},
-    layout::{Axis, BarMode, BoxMode, Layout, Margin},
-    Bar, BoxPlot, Histogram, Plot, Scatter,
+    layout::{Axis, BarMode, BoxMode, Layout, Margin, ViolinMode},
+    violin::{MeanLine, ViolinBox, ViolinPoints, ViolinSide},
+    Bar, BoxPlot, Histogram, Plot, Scatter, Violin,
 };
 use plotly_utils::write_example_to_html;
 use rand_distr::{Distribution, Normal, Uniform};
@@ -477,6 +478,98 @@ fn fully_styled_box_plot(show: bool, file_name: &str) {
 }
 // ANCHOR_END: fully_styled_box_plot
 
+// Violin Plots
+// ANCHOR: basic_violin_plot
+fn basic_violin_plot(show: bool, file_name: &str) {
+    let y = vec![
+        0.2, 0.2, 0.6, 1.0, 0.5, 0.4, 0.2, 0.7, 0.9, 0.1, 0.5, 0.3, 0.8, 0.4, 0.6,
+    ];
+
+    let trace = Violin::new(y)
+        .box_plot(ViolinBox::new().visible(true))
+        .mean_line(MeanLine::new().visible(true))
+        .name("Total");
+
+    let layout = Layout::new().title("Basic Violin Plot");
+
+    let mut plot = Plot::new();
+    plot.set_layout(layout);
+    plot.add_trace(trace);
+
+    let path = write_example_to_html(&plot, file_name);
+    if show {
+        plot.show_html(path);
+    }
+}
+// ANCHOR_END: basic_violin_plot
+
+// ANCHOR: horizontal_violin_plot
+fn horizontal_violin_plot(show: bool, file_name: &str) {
+    let x = vec![1.4, 2.1, 1.9, 3.2, 2.7, 2.2, 1.8, 2.5, 3.1, 2.0, 2.6, 1.7];
+
+    let trace = Violin::<f64, f64>::default()
+        .x(x)
+        .points(ViolinPoints::All)
+        .box_plot(ViolinBox::new().visible(true))
+        .mean_line(MeanLine::new().visible(true))
+        .orientation(Orientation::Horizontal)
+        .name("Score");
+
+    let layout = Layout::new().title("Horizontal Violin Plot");
+
+    let mut plot = Plot::new();
+    plot.set_layout(layout);
+    plot.add_trace(trace);
+
+    let path = write_example_to_html(&plot, file_name);
+    if show {
+        plot.show_html(path);
+    }
+}
+// ANCHOR_END: horizontal_violin_plot
+
+// ANCHOR: split_violin_plot
+fn split_violin_plot(show: bool, file_name: &str) {
+    let x = vec![
+        "Mon", "Mon", "Mon", "Mon", "Tue", "Tue", "Tue", "Tue", "Wed", "Wed", "Wed", "Wed",
+    ];
+
+    let trace1 = Violin::new_xy(
+        x.clone(),
+        vec![0.6, 0.9, 0.4, 0.7, 0.8, 1.1, 0.6, 0.9, 1.0, 1.3, 0.8, 1.1],
+    )
+    .legend_group("Yes")
+    .scale_group("Yes")
+    .name("Yes")
+    .side(ViolinSide::Negative)
+    .line(Line::new().color(NamedColor::Blue));
+
+    let trace2 = Violin::new_xy(
+        x,
+        vec![0.4, 0.7, 0.3, 0.5, 0.6, 0.9, 0.4, 0.7, 0.8, 1.1, 0.6, 0.9],
+    )
+    .legend_group("No")
+    .scale_group("No")
+    .name("No")
+    .side(ViolinSide::Positive)
+    .line(Line::new().color(NamedColor::Green));
+
+    let layout = Layout::new()
+        .title("Split Violin Plot")
+        .violin_mode(ViolinMode::Overlay);
+
+    let mut plot = Plot::new();
+    plot.set_layout(layout);
+    plot.add_trace(trace1);
+    plot.add_trace(trace2);
+
+    let path = write_example_to_html(&plot, file_name);
+    if show {
+        plot.show_html(path);
+    }
+}
+// ANCHOR_END: split_violin_plot
+
 // Histograms
 fn sample_normal_distribution(n: usize, mean: f64, std_dev: f64) -> Vec<f64> {
     let mut rng = rand::rng();
@@ -729,6 +822,11 @@ fn main() {
     grouped_horizontal_box_plot(false, "grouped_horizontal_box_plot");
     fully_styled_box_plot(false, "fully_styled_box_plot");
 
+    // Violin Plots
+    basic_violin_plot(false, "basic_violin_plot");
+    horizontal_violin_plot(false, "horizontal_violin_plot");
+    split_violin_plot(false, "split_violin_plot");
+
     // Histograms
     basic_histogram(false, "basic_histogram");
     horizontal_histogram(false, "horizontal_histogram");

plotly/src/common/mod.rs

@@ -232,6 +232,7 @@ pub enum PlotType {
     Pie,
     Treemap,
     Sunburst,
+    Violin,
 }
 
 #[derive(Serialize, Clone, Debug)]

plotly/src/lib.rs

@@ -61,13 +61,13 @@ pub use plot::{Plot, Trace, Traces};
 // Also provide easy access to modules which contain additional trace-specific types
 pub use traces::{
     box_plot, contour, heat_map, histogram, image, mesh3d, sankey, scatter, scatter3d,
-    scatter_mapbox, sunburst, surface, treemap,
+    scatter_mapbox, sunburst, surface, treemap, violin,
 };
 // Bring the different trace types into the top-level scope
 pub use traces::{
     Bar, BoxPlot, Candlestick, Contour, DensityMapbox, HeatMap, Histogram, Image, Mesh3D, Ohlc,
     Pie, Sankey, Scatter, Scatter3D, ScatterGeo, ScatterMapbox, ScatterPolar, Sunburst, Surface,
-    Table, Treemap,
+    Table, Treemap, Violin,
 };
 
 pub trait Restyle: serde::Serialize {}

plotly/src/traces/mod.rs

@@ -21,6 +21,7 @@ pub mod sunburst;
 pub mod surface;
 pub mod table;
 pub mod treemap;
+pub mod violin;
 
 pub use bar::Bar;
 pub use box_plot::BoxPlot;
@@ -42,5 +43,6 @@ pub use sunburst::Sunburst;
 pub use surface::Surface;
 pub use table::Table;
 pub use treemap::Treemap;
+pub use violin::Violin;
 
 pub use self::image::Image;