Fix plot labels with spaces

[Enchufa2]

Closes #297. @edzer I simplified a bit the logic to add units to labels, with some changes:

• ~I don't think we should export make_unit_label anymore. This was probably exported to enable ggforce to set the labels easily, right? But it was not used correctly anyway. Now that we have included ggforce's functionality, I have renamed the function as make_unit_label_internal and deprecated direct calls to make_unit_label (which calls the former one) if this is ok with you. Or are you aware of any other package really requiring make_unit_label?~ See below.
• The specific fix for #297 is included in make_unit_label, which replaces spaces with ~ if the label is a string.
• Previously, units were not added if the user provided a custom label (via xlab, ylab). Instead, I think that we should always add units, as implemented in this PR. And if the user do not want units, they should just drop them.

[Enchufa2]

Examples:

library(units)
#> udunits database from /usr/share/udunits/udunits2.xml
library(ggplot2)

mtcars$consumption <- set_units(mtcars$mpg, mi / gallon)
mtcars$power <- set_units(mtcars$hp, hp)

plot(consumption~power, mtcars, xlab="asdf asdf")

p <- ggplot(mtcars) + geom_point(aes(power^2, consumption))
p + xlab("some^2 custom stuff")

p + xlab(NULL)

^{Created on 2022-01-20 by the reprex package (v2.0.1)}

[codecov[bot]]

Codecov Report

Merging #298 (66590e7) into main (729bc9c) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #298   +/-   ##
=======================================
  Coverage   92.24%   92.25%           
=======================================
  Files          19       19           
  Lines         916      917    +1     
=======================================
+ Hits          845      846    +1     
  Misses         71       71           

Impacted Files	Coverage Δ
R/plot.R	97.22% <100.00%> (-0.08%)	:arrow_down:
R/scale_units.R	89.13% <100.00%> (+0.49%)	:arrow_up:

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[bart1]

Thank you for your effort @Enchufa2 I have played around a bit with specifying the labels, spaces and expressions work as expected. The results for special characters in the string (e.g. \n and \t) still differ. These are maybe not as critical to get right but if it is easy it might prevent errors for people.

require(units)
#> Loading required package: units
#> udunits database from /usr/share/xml/udunits/udunits2.xml
d<-data.frame(b=1:5,a=set_units(5:1,'Hz'))
require(ggplot2)
#> Loading required package: ggplot2
ggplot(d)+geom_point(aes(a,b))+xlab("a b")+ylab("a b")

ggplot(d)+geom_point(aes(a,b))+xlab("a\nb")+ylab("a\nb")

ggplot(d)+geom_point(aes(a,b))+xlab("a\tb")+ylab("a\tb")

ggplot(d)+geom_point(aes(a,b))+xlab(expression(frac(a,b)))+ylab(expression(frac(a,b)))

^{Created on 2022-01-20 by the reprex package (v2.0.1)}

[Enchufa2]

Thanks for testing. To be able to properly show powers, unit labels must be expressions, and thus we lose the ability to insert a newline or a tab character.

[bart1]

Thanks those new lines could be solved by expressions anyway

[Enchufa2]

There are projects using make_unit_label after all... Let's undeprecate it then. :(

[Enchufa2]

Done, so if no further comments from @edzer, we are good to go. :)

[edzer]

Looks good to me - great work!