Add stack=:dodge and stack=:waterfall to barplot to allow easy waterfall charts creation

[daschw]

Description

This PR implements the options

barplot(...; stack=:waterfall, ...)
barplot(...; stack=:dodge, ...)

I frequently use what some people call waterfall charts (plotly, python) to visualize individual positive and negative components that add up to a net result.

Suppose I have a vector y of such components and colors c to indicate the sign.

using CairoMakie
green, red = Makie.wong_colors()[[3, 6]]
y = [3, 2, 1, -4, 1, -3, -2, 4, -1, 3]
c = map(v -> v < 0 ? red : green, y) # color bars by sign

To achieve something similar with Makie I can recalculate stacked y values and corresponding fillto values.

y_waterfall = cumsum(y)
fill_waterfall = [0; y_waterfall[1:end-1]]
barplot(y_waterfall, color=c, fillto=fill_waterfall)

With this PR I can do the same thing with just:

barplot(y, color=c, stack=:waterfall)

Now suppose I want to compare multiple net results grouped by x with individual components grouped by dodge.

x = repeat(1:2, inner=5)
dodge = repeat(1:5, outer=2)

Here I have to preprocess my data in some way like this:

y_dodge = similar(y)
fill_dodge = similar(y)
for i in unique(x)
    inds = findall(==(i), x)
    y_dodge[inds] .= cumsum(y[inds])
    fill_dodge[inds] .= [0; y_dodge[inds][1:end-1]]
end
barplot(x, y_dodge, color=c, dodge=dodge, fillto=fill_dodge)

It would be even more cumbersome if x and dodge were not sorted properly. This PR enables me to just use:

barplot(x, y, color=c, dodge=dodge, stack=:dodge)

I'm not really sure about the name choices :waterfall and :dodge though and open to better suggestions.
Something similar was also asked for in https://discourse.julialang.org/t/waterfall-plot-makie-jl/79988.

Type of change

Delete options that do not apply:

• New feature (non-breaking change which adds functionality)

Checklist

• Added an entry in NEWS.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[jkrumbiegel]

Thanks for the PR! My recurring feeling with barplot is that it kind of handles too much, all the stacking, dodging, labelling. Wouldn't a waterfall recipe work as well? Or is that not good because you then need to implement dodging again?

[daschw]

My recurring feeling with barplot is that it kind of handles too much, all the stacking, dodging, labelling.

Yeah, I was expecting these concerns with this PR and I totally understand them.

Wouldn't a waterfall recipe work as well? Or is that not good because you then need to implement dodging again?

Sure, this would work as well. I guess I wouldn't even have to reimplement dodging, because I could use barplot in the waterfall recipe and just calculate corresponding y and fillto values, right?. I'm not sure if you are suggesting a waterfall recipe for my personal use or as addition to Makie. In the second case, I could rewrite this PR. I was already thinking of this alternative, but I decided to hook into barplot, because it seemed like the smaller change.

[jkrumbiegel]

Yes as a recipe in Makie on top of barplot. I thought the up down coloring scheme from the waterfall might need its own logic anyway? Or is that not the typical mode of using it

[daschw]

closed by #2416