Manual legend labels

[jkrumbiegel]

Allows to use visual(label = ...) to include layers in the legend without them using any legendable scales. Otherwise, adding layers that are included in the legend always requires making one-element categorical scales, which is an annoying overhead. And it's arbitrary what scale to use for a one-element legend, but of course the scale chosen affects the visual output. For example, if one wants a line with default color, you cannot use the color aesthetic because that will override the color. So you kind of arbitrarily would have to use linestyle or something else. With the label keyword, this is much simpler:

df_subjects = (; x = repeat(1:10, 10), y = cos.(1:100), id = repeat(1:10, inner = 10))
df_func = (; x = range(1, 10, length = 20), y = cos.(range(1, 10, length = 20)))
    
spec1 = data(df_subjects) * mapping(:x, :y, group = :id => nonnumeric) * visual(Lines, linestyle = :dash, color = (:black, 0.2), label = "Subject data")
spec2 = data(df_func) * mapping(:x, :y) * (visual(Lines, color = :tomato) + visual(Scatter, markersize = 12, color = :tomato, strokewidth = 2)) * visual(label = L"\cos(x)")
    
draw(spec1 + spec2)