Plots.jl: wrong :letter for some plot recipes

[briochemc]

There is an issue with :letter for some recipes that take a single argument. This is because the data of single-argument plots lives on different axes depending on the plot recipe. For instance:

• plot(x): x lives in the y axis, :letter == :y ✔️
• histogram(x) or vline(x): x lives in the x axis, but :letter == :y ✖️

Maybe there are other similar cases.

To illustrate this with MWEs, take this recipe, which just displays the :letter in the title for MyType arrays:

using Plots, RecipesBase
struct MyType <: Number
    val::Float64
end
value(m::MyType) = m.val
@recipe function f(::Type{T}, m::T) where T <: AbstractArray{<:MyType}
    title --> string(length(m), " ", plotattributes[:letter], "-axis values")
    value.(m)
end

Then

histogram(MyType.(randn(1000)))

gives

and

vline(MyType.(randn(10))

gives

[daschw]

Yeah, we should find a general solution for that. Maybe some kind of switch_axes trait for seriestypes defined in RecipesBase.
For now a workaround in the recipe would be something like

switch = get(plotattributes, :seriestype, :path) in (:histogram, :vline)
letter = plotattributes[:letter]
if switch
    letter == :x && (letter = :y)
    letter == :y && (letter = :x)
end

Maybe we should rather do this in type recipe processing in Plots, though.

[briochemc]

Yes, I imagined I could do something like that but it seems like you'd rather have this been done for all axis-aware type recipes by default, right? I also don't know all the :seriestype out there that need that switch. Are :histogram and :vline the only ones?

[daschw]

Yes, thanks for bringing this up! It's probably better if we fix this in Plots.
I think there's also some more histogram-like seriestypes like :stephist.

[briochemc]

Could you point out to how I could help with this tiny bug?

[BeastyBlacksmith]

Wouldn't be the best solution to redirect, e.g. vline(x) to plot(x,[], seriestype=:vline)?
And edit the vline recipe accordingly?

[briochemc]

I'm sorry if this sounds like a dumb question, but could you clarify how one "redirects" vline(x)? I think I need a bit of hand-holding! 😅

Also, are these changes supposed to happen in Plots.jl? If yes in which files? (The code base of Plots.jl is quite large to me so I often get lost looking for things inside of it.) If not should I be looking at RecipesBase or another package?

[BeastyBlacksmith]

The vline recipe is defined here and the shorthand is defined here.
The @shorthands macro expands to something like vline(args... ;kwargs...) = plot(args... ; seriestype=:vline, kwargs...) and the issue here is that plot(x) is treated like plot(1:length(x), x), so we explicitly need to add a more specific method for the one argument vline that passes its data as x and not as y.
Other workaround might be to simply add letter := :x in the vline-recipe.