key for linestyle

[bjarthur]

@Mattriks you've done a lot with the key, but i don't recall if you have plans to work on including linestyle. i have a need for both color and linestyle in the key, and can devote some time to implement. wanted to check with you first though.

using Gadfly, DataFrames
df = DataFrame(y=1:8,
               x=repeat([1, 2], 4),
               c=repeat(["a","b"], inner=4),
               ls=repeat(["c","d"], inner=2, outer=2))
plot(df, x=:x, y=:y, color=:c, linestyle=:ls, Geom.line) |> SVG("test.svg")

[Mattriks]

Something that I was working towards (when I use to have time!), was to switch the discrete color aesthetic to use render_discrete_key (#1385), i.e. replace render_discrete_color_key. I would like to get back to that sometime. Yes Guide.linekey is also needed. I haven't thought about the best way to implement, but my first guess would be to make render(guide::LineKey, theme, aes) call render_discrete_key with line shapes. Similar to how Guide.shapekey and Guide.sizekey work. The alternative would be for Guide.linekey to have it's own render_discrete_linekey, but not sure that's preferable than developing render_discrete_key to work with lines.

[DomHin]

Will this be done within the next 3-5 months?
I am starting to write my PhD Thesis and this would be very helpful.
Thanks for your work on that @Mattriks :)

[bjarthur]

i'm getting some unexpected and inconsistent output when using the shape, size, color, and linestyle aesthetics. i would expect plot(x=[1,2,3,1,2,3], y=[1,2,3,4,5,6], XXX=[1,1,1,2,2,2], Geom.line, Geom.point), where XXX is one of those four aesthetics, to all have two lines, a key, and be discrete, yet each is not so in a different way.

with shape there is just one line:

with size there is also just one line, and no key:

with color it is continuous:

with linestyle there is no key:

@Mattriks do you concur that these are all bugs? if so, what can we change and still respect semantic versioning?

[bjarthur]

discrete colors is easy of course. just add Scale.color_discrete. what is the argument that this should not be the default when typeof(color)<:Vector{Int}?

a size key is a bit more cumbersome with Scale.size_discrete2(n->range(3pt, 8pt, length=n)). strange that Scale.size_discrete is not good enough, and that anything extra is needed at all. what is the argument that we can't supply sensible defaults?

[Mattriks]

Here are some answers to your q's:

• Currently Geom.line maps to aesthetics: group, color and linestyle (the Tutorial table shows the respective Scales). See my example plot below.
• A long-term plan is to make Theme line_width a proper aesthetic (e.g. see PR1521). Size and linewidth should be kept separate.
• Yes to get the sizekey, you need to add Scale.size_discrete2, Scale.size_radius or Scale.size_area (see Size revamp 1: Scale.size_discrete2 #1376, Size revamp 2: Guide.sizekey #1379, Size revamp3: ContinuousSizeScale #1386). These new Scales are written to be consistent with other aesthetic/Scales, and to fix certain problems, including the first item in Roadmap #1385 (tbd).

what is the argument that we can't supply sensible defaults? (not clear what you mean here)

• For color, the preference to map integers to discrete variables is mentioned in Option 1) in Color aesthetic mapping syntax #1430.

# Shape applies to points not lines. What shape is a line? 🤔

shape = [1,1,1,2,2,2]
plot(x=[1,2,3,1,2,3], y=[1,2,3,4,5,6], group=shape, shape=shape, Geom.line, Geom.point)

[bjarthur]

• Yes to get the sizekey, you need to add Scale.size_discrete2, Scale.size_radius or Scale.size_area (see Size revamp 1: Scale.size_discrete2 #1376, Size revamp 2: Guide.sizekey #1379, Size revamp3: ContinuousSizeScale #1386). These new Scales are written to be consistent with other aesthetic/Scales, and to fix certain problems, including the first item in Roadmap #1385 (tbd).

what is the argument that we can't supply sensible defaults? (not clear what you mean here)

it's not intuitive that one automatically gets a key for shape (w/o adding Scale.shape_discrete) but that for size one needs to add a scale. is there a reason for this design? why can't we just automatically include Scale.size_discrete2 if the aesthetic is discrete?

[Mattriks]

The current issue with size is that the default size scale is Scale.size_discrete (or Scale.size_continuous), which does not trigger Guide.sizekey. The plan is to replace Scale.size_discrete with Scale.size_discrete2 in Gadfly 2.0 (see #1376). I mentioned that in ?Scale.size_continuous, but should have also mentioned it in ?Scale.size_discrete . The Tutorial Table also contains useful info about the differences.

[RossBoylan]

The discussion seems to have expanded and wandered from the title. But that title, and the question

with linestyle there is no key:
...
@Mattriks do you concur that these are all bugs?

is exactly my current concern. The subsequent responses address some the other issues mentioned, but not the basic provision of a key for linestyle that I can see.

It seems even the gallery exhibiting https://docs.juliahub.com/Gadfly/DvECm/1.3.2/gallery/scales/#[Scale.linestyle_discrete](@ref) shows a graph that has nothing on it explaining what the different linestyles mean, i.e., it just illustrates that the feature doesn't work.

I would expect Scale.linestyle_discrete() to produce a little legend that indicated what each type of linestyle meant. That's what I've been looking for in some graphs produced most recently with

plot(pdat, x=:σ, y=:MSEP, color=:τ, linestyle=:pred, Scale.color_discrete(), Geom.line, Scale.linestyle_discrete(order=[1, 2]))

where the values of pred are one of two short strings.

Is this a bug? Perhaps I've misunderstood something.

My example does raise an additional complication, what color (and potentially other aesthetics) to use for the linestyles. I think this is the same issue one would confront if making a legend for shapes, or sizes, or other things the package already manages. I'd be fine with black or even a random selection from the colors used in the plot.