Julia Plotting: delete and modify existing lines

Question

Two questions in one: Given a line plotted in Julia, how can I

1. delete it from the plot and legend (without clearing the whole plot)
2. change its properties (such as color, thickness, opacity)

As a concrete example in the code below, how can I 1. delete previous regression lines OR 2. change their opacity to 0.1?

using Plots; gr()

f = x->.3x+.2
g = x->f(x)+.2*randn()

x = rand(2)
y = g.(x)
plt = scatter(x,y,c=:orange)
plot!(0:.1:1, f, ylim=(0,1), c=:green, alpha=.3, linewidth=10)

anim = Animation()
for i=1:200
    r = rand()
    x_new, y_new = r, g(r)
    push!(plt, x_new, y_new)
    push!(x, x_new)
    push!(y, y_new)
    A = hcat(fill(1., size(x)), x)
    coefs = A\y
    plot!(0:.1:1, x->coefs[2]*x+coefs[1], c=:blue)  # plot new regression line
    # 1. delete previous line
    # 2. set alpha of previous line to .1
    frame(anim)
end
gif(anim, "regression.gif", fps=5)

I tried combinations of delete, pop! and remove but without success. A related question in Python can be found here: How to remove lines in a Matplotlib plot

Answer 1

Here is a fun and illustrative example of how you can use pop!() to undo plotting in Julia using Makie. Note that you will see this goes back in the reverse order that everything was plotted (think, like adding and removing from a stack), so deleteat!(scene.plots, ind) will still be necessary to remove a plot at a specific index.

using Makie

x = range(0, stop = 2pi, length = 80)
f1(x) = sin.(x)
f2(x) = exp.(-x) .* cos.(2pi*x)
y1 = f1(x)
y2 = f2(x)

scene = lines(x, y1, color = :blue)
scatter!(scene, x, y1, color = :red, markersize = 0.1)

lines!(scene, x, y2, color = :black)
scatter!(scene, x, y2, color = :green, marker = :utriangle, markersize = 0.1)

display(scene)

sleep(10)
pop!(scene.plots)
display(scene)

sleep(10)
pop!(scene.plots)
display(scene)

You can see the images above that show how the plot progressively gets undone using pop(). The key idea with respect to sleep() is that if we were not using it (and you can test this on your own by running the code with it removed), the fist and only image shown on the screen will be the final image above because of the render time.

You can see if you run this code that the window renders and then sleeps for 10 seconds (in order to give it time to render) and then uses pop!() to step back through the plot.

Docs for sleep()