Map or set segment_colour and segment_alpha

[jiho]

This was made possible before by pull-request #29 but was then overridden by other commits. These changes are inspired by geom_boxplot and take the best of both worlds: map to colour and alpha of text by default but allow to override with a fixed value.

[slowkow]

ggplot(
    mtcars,
    aes(x = wt, y = mpg, label = rownames(mtcars), colour = factor(cyl))
  ) +
  geom_point() +
  geom_text_repel()

Before this pull request (dark grey line segments):

After this pull request (line segment color matches text color):

[slowkow]

@jiho Thank you very much for your pull request! I appreciate it.

Can I ask you to please confirm that this is your desired behavior for this pull request? I wonder if you intended to change the border of the label with the alpha option, or if you intended to leave the border unchanged.

ggplot(
    mtcars,
    aes(x = wt, y = mpg, label = rownames(mtcars), colour = factor(cyl))
  ) +
  geom_point() +
  geom_label_repel(alpha = 0.33)

Before this pull request:

It seems that only the background color of the label is affected by the alpha option. Meanwhile, the text color and the segment color are unchanged.

After this pull request:

It seems that the segment color matches the text color. Also, the alpha option is now changing 3 things: the segment, the text, and the label background. It seems that the border of the label is unchanged.

[jiho]

Hum, seems OK for geom_text_repel but not for geom_label_repel. I intended alpha to change everything.

Let me check against geom_label and edit the pull request accordingly (I am not very familiar with geom_label).

[jiho]

In geom_label, alpha only controls the background opacity. I don't like it (if I want to hide stuff, I want to hide everything, not just the background) but you probably want to be consistent with ggplot2. I'll update the pull request to be similar to geom_label for now and will submit a PR to ggplot2 to make everything transparent.

[slowkow]

I think I agree with your judgment that alpha should modify the transparency of everything, including text, background color, border color, and segment color.

I'm happy to go ahead and merge your pull request with this new behavior.

It looks like this:

[jiho]

Great, thanks. That looks good indeed!

The inability to change separately the colour of the text and of the outline is a bit bothersome but again, this is the same for geom_label

Thanks for being so reactive (and for ggrepel!)

[aphalo]

I seem to remember that at some point during development of ggplot 2.0.0 alpha was changed to affect everything but then a decision was made to go back to the original behaviour. The main problem seems to be bar plots and "point" shapes like 21, 22, and 23, for which one usually wants to retain solid borders while making the fill transparent.
Found!
tidyverse/ggplot2#1371
tidyverse/ggplot2#1523

[jiho]

Thanks for the precision. While it may make sense for geom_density() I see little reason not to have alpha affect the whole label here. Anyhow, we'll see how Hadley reacts, the change is submitted: tidyverse/ggplot2#1924 (it was pretty easy!)

[slowkow]

@aphalo Thank you for those links! I think I'm comfortable letting alpha control all properties of a label (text, background, border, segment). Perhaps alpha should behave differently for point, bar, or density.

@jiho Just a small note: your pull request changed the appearance of one of my vignette figures. This is OK with me, because I can change the segment color with segment.color = 'grey50'.

Before pull request

After pull request

Ater pull request, segment.color = 'grey50'

[aphalo]

@slowkow Yes, I agree with you about label. @jiho I was mostly thinking about a PR for ggplot2. It will need good argumentation to have a chance of being accepted. @jiho @slowkow If rejected for ggplot2, could a label_fixed that behaves with respect to alpha exactly as label_repel be added to ggrepel?

[slowkow]

Instead of adding a new function

ggplot(...) + geom_label_fixed()

I would recommend

ggplot(...) + geom_label_repel(..., max.iter = 0)

[aphalo]

Yes, of course! Thanks!

[jiho]

All this makes me think that really there should be separate aesthetics, than can be set or mapped separately, for each plot element: segment.colour, text.colour, label.colour, label.fill, segment.alpha, etc. with some basic inheritance rules (i.e. setting colour sets both text.colour and label.colour, but if both colour and label.colour are set, label.colour takes precedence for the label). What is done here (and in geom_boxplot, etc.) allows the inheritance, allows to set aesthetics but does not allow to map separately. I'm not sure this is at all possible in ggplot2 (colour, fill, etc. have a special status but I can't find where it is defined).

[jiho]

Also, to simplify things, both in code and visually, I would have defaulted to coloured labels with no stroke with fill setting the inside colour and colour setting the text colour. But again, you probably want to be compatible with ggplot2 there.

[aphalo]

@jiho Yes, very true. Visually a lot cleaner! I think if one wants to keep compatibility, one could have a geom behaving like you suggest under a different name. Most of the code could be shared, I think. (But today it seems only new geoms come to my mind.)

[aphalo]

@jiho Or would removing the border line/stroke of the labels be better handled as a theme setting?