2D Histogram Overlaid with a Scatter Chart

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

Section

Combining a Histogram2d with a Scatter trace on the same axes lets you see both the density distribution and the individual data points at once. Set opacity on the histogram to let the scatter points show through.

alias Plotly.{Figure, Histogram2d, Scatter}

: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 = 200
x = gen.(n)
y = gen.(n)

Figure.new()
|> Figure.add_trace(
  Histogram2d.new(
    x: x, y: y,
    colorscale: "YlOrRd",
    opacity: 0.7
  )
)
|> Figure.add_trace(
  Scatter.new(
    x: x, y: y,
    mode: "markers",
    marker: %{color: "white", size: 4, opacity: 0.5}
  )
)
|> Figure.update_layout(title: "2D Histogram Overlaid with Scatter")
|> Plotly.show()