2D Histogram Contour Plot with Histogram Subplots (Slider Control)

Mix.install([
  {:plotly_ex, "~> 0.3"},
  {:kino, "~> 0.18"}
])

Section

A Histogram2dcontour in the centre with marginal Histogram traces on the top and right. The layout.sliders widget (same technique as custom_controls/09_basic_slider.livemd) uses method: "restyle" to update the ncontours property on the contour trace in real time — no JavaScript callbacks required.

Subplot domains:

alias Plotly.{Figure, Histogram, Histogram2dcontour}

:rand.seed(:exsss, {1, 2, 3})

gen = fn n ->
  for _ <- 1..n do
    (for _ <- 1..12, do: :rand.uniform()) |> Enum.sum() |> Kernel.-(6.0)
  end
end

n = 500
x = gen.(n)
y = gen.(n)

ncontours_values = [3, 5, 10, 15, 20, 30]

slider_steps =
  for {nc, _i} <- Enum.with_index(ncontours_values) do
    %{
      method: "restyle",
      label: "#{nc}",
      args: [%{ncontours: nc}, [0]]
    }
  end

# Default active index — ncontours = 20 is index 4
default_index = Enum.find_index(ncontours_values, &(&1 == 20))

Figure.new()
|> Figure.add_trace(
  Histogram2dcontour.new(
    x: x, y: y,
    ncontours: 20,
    colorscale: "Blues",
    reversescale: true,
    showscale: false,
    xaxis: "x",
    yaxis: "y"
  )
)
|> Figure.add_trace(
  Histogram.new(
    x: x,
    xaxis: "x",
    yaxis: "y2",
    showlegend: false,
    marker: %{color: "rgba(31, 119, 180, 0.7)"}
  )
)
|> Figure.add_trace(
  Histogram.new(
    y: y,
    xaxis: "x2",
    yaxis: "y",
    showlegend: false,
    marker: %{color: "rgba(31, 119, 180, 0.7)"}
  )
)
|> Figure.update_layout(
  title: "2D Contour Histogram with Marginals — Slider Controls Contour Count",
  showlegend: false,
  autosize: false,
  width: 600,
  height: 580,
  margin: %{t: 60, l: 50, r: 20, b: 110},
  hovermode: "closest",
  bargap: 0,
  xaxis: %{domain: [0, 0.85], showgrid: false, zeroline: false, title: "x"},
  yaxis: %{domain: [0, 0.85], showgrid: false, zeroline: false, title: "y"},
  xaxis2: %{domain: [0.85, 1], showgrid: false, zeroline: false},
  yaxis2: %{domain: [0.85, 1], showgrid: false, zeroline: false},
  sliders: [%{
    steps: slider_steps,
    active: default_index,
    currentvalue: %{prefix: "Contours: ", visible: true, xanchor: "center"},
    pad: %{t: 60, b: 10}
  }]
)
|> Plotly.show()