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🍊 :bar_chart: :bulb: Orange: Interactive data analysis
https://orangedatamining.com
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Scatter Plot (and related plots, such as Network Explorer): allow distiguishing more than 10 categories by color #6622

Open wvdvegte opened 10 months ago

wvdvegte commented 10 months ago

What's your use case? I would like to be able to visualize more than 10 categories of a categorical variable by color in Scatter Plot .

What's your proposed solution? In Annotated Corpus Map (Text add-on), it is possible to color more than 10 clusters if "Color points by cluster" is checked, so it shouldn't be too difficult to support more categories.

Are there any alternative solutions? Not that I know of.

janezd commented 10 months ago

TL;DR: Why show you more colors than you can actually distinguish in a plot?

This issue has a lot of history and discussions

We decided to use colors that are distinguishable; one of criteria was that they must be "nameable" (e.g. have names in English). The "lighter shade of cyan" is probably indistinguishable from the darker shade. Colors like in https://artshacker.com/wp-content/uploads/2014/12/Kellys-22-colour-chart.jpg are useless because I can't distinguish between reddish orange and red. In particular not if they are scattered around the plot.

Here is a nicer palette: https://sashamaps.net/docs/resources/20-colors/. Still, we can't use white, I would also remove two greens, two of pink-purple-magenta-lavender, one brown and This leaves us with 14 colors. (Just 4 more than 10!)

So far, one could still say that this is, well, not our problem. Let Orange show as many colors as necessary and let the user deal with it.

But the problem is: what if you need just two or three? Or, perhaps, five? The palette must be "progressive" in the sense that a palette used for n groups must contain all the colors that would be used for n-1 groups. Imagine that the user picks two subgroups, like two clusters in a dendrogram. They get assigned some colors in a subsequent plot. If he then picks another subgroup, the plot must still show the same two colors plus another one. And so forth.

Colors in a 20-color (or 14-color) palette are chosen so that they are as distinct as possible. The blue in this palette is quite ugly - but this is done to distinguish it from navy. So if we take this palette, we'll have to live with ugly red and blue in most plots just to accommodate 20 (14) colors in the rare cases one would need them.

All this led us to set a reasonable number of distinguishable colors that look nice and work well when progressively increasing the number of groups. As a consequence, we merge other, less frequent groups into "Other".

The issue is still open for discussion, but my worry is that we already walked this path (not just of discussion but of actually implementation in Orange) a few times and I would prefer not to go another circle. :)

wvdvegte commented 10 months ago

I ran into this while I was actually using Network Explorer, not Scatter Plot. I realize that like Annotated Corpus Map, which does allow more than 20 colors, Network Explorer has extra graphical elements that can help the viewer deal with hard-to-distinguish colors. ACP can show cluster hulls to help dealing with this, and NE has the network connections. I agree that for Scatter Plot it might not make sense, but I think for Network Explorer it does.

janezd commented 10 months ago

We had a long discussion today.

  1. I believe that the result was that current behavior should remain the default, but the user should be given an opportunity to have as many colors as (s)he wants. The resulting palette would be a continuation of the current palette, and we won't care much if the colors are difficult to distinguish.
  2. Scatterplot(-like) widgets already have many options so a better place to put a corresponding checkbox (grouping vs. showing all colors) would be in the Color widget. There may be alternative places, but whoever implements this should prudently show others a prototype.
  3. Which brings us to the last point: as the one who implemented palettes, the Color widget and everything related, I'm the obvious candidate to add this functionality, but I'm not a fan of it. :) Somebody else will have to do it. In other words, this may have to wait for some time before it will really hurts some developer who knows how to make this change. :) (While at it, this can be done at the same time as inverting palettes, #6586 - the changes are similar and at the same places.)