Allow absolute width for geom_errorbar (and possibly others)

[marcpabst]

Currently, the width argument for geom_errorbar only sets the relative size of the whiskers. It would be really helpful to have an option to specify the whisker size in absolute units. This would make it easier to maintain consistent whisker dimensions across plots, regardless of the scale or data range.

[alshan]

We maybe can have an additional parameters width_unit and height_unit. Or just one cap_unit, accepting "px" or "lw":

geom_errorbar(width = 5, cap_unit = "px")   # 5 pixels
geom_errorbar(width = 3, cap_unit = "lw")   # 3 * linewidth

Would it do?

[marcpabst]

I think that would be helpful. My main use case are plots with a varying of discrete data points on the x axis, which look weird with uber-long whiskers. If I remember correclty, Makie.jl does something similar, where you can specify the reference frames for x and y values independently, which comes in very handy sometimes.

[alshan]

Ok, and you've mentioned "and possibly others" in the title. Are you referring to boxplot?

[alshan]

Interesting, there is whisker_width parameter in geom_boxplot

Same in geom_errorbar could work as well I guess.

[marcpabst]

geom_boxplot, and possibly even geom_bar()? Basically, everything where there is a width parameter, and one could reasonably want to specify the size in absolute units (although I'm admittedly struggling to come up with a good use case for geom_bar()). Another related thing is specifying absolute units for something like geom_label(), which I often use for annotations but currently can only be specified in data coordinates. Maybe it's worth finding a more general solution to this?

Here's what Makie.jl is doing: https://docs.makie.org/v0.22/explanations/conversion_pipeline#Coordinate-spaces