Lasso Selection

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

Section

Lasso and box select are built into the Plotly.js toolbar. In Livebook, selected points can be captured via the plotly_selected event using PlotlyLive.subscribe/2 from Batch 1.

Click the lasso or box-select toolbar icon, draw a selection on the chart, then evaluate the receive cell to see the selected points.

alias Plotly.{Figure, Scatter}
alias Plotly.Kino.PlotlyLive

:rand.seed(:exsplus, {42, 0, 0})
n = 80
x = Enum.map(1..n, fn _ -> :rand.normal() * 2 end)
y = Enum.map(1..n, fn _ -> :rand.normal() * 2 end)

chart =
  Figure.new()
  |> Figure.add_trace(Scatter.new(
    x: x,
    y: y,
    mode: "markers",
    marker: %{size: 10, color: "steelblue", opacity: 0.7}
  ))
  |> Figure.update_layout(
    title: "Use lasso/box select tool, then run next cell",
    dragmode: "lasso"
  )
  |> PlotlyLive.new()

PlotlyLive.subscribe(chart, :selection, :selected)
chart

# Draw a selection above, then evaluate this cell
receive do
  {:selection, %{"data" => %{"points" => pts}}} ->
    IO.puts("Selected #{length(pts)} points")
    Enum.each(pts, fn p -> IO.puts("  x=#{p["x"]}, y=#{p["y"]}") end)
after
  15_000 -> "No selection within 15 s — use the lasso tool first"
end