integrate ggplot2 scales, closes #164

[Enchufa2]

@edzer I've adapted the code from ggforce and added Thomas as a contributor in the DESCRIPTION. I've called the functions scale_*_units instead of scale_*_unit to follow the naming conventions. I've also dropped ggforce from the DESCRIPTION, demos and vignettes, but preserving the mention in the ACKs (i.e., this). Is that ok?

[codecov[bot]]

Codecov Report

Merging #294 (115a54f) into main (8497cc0) will decrease coverage by 0.21%. The diff coverage is 88.63%.

@@            Coverage Diff             @@
##             main     #294      +/-   ##
==========================================
- Coverage   93.15%   92.93%   -0.22%     
==========================================
  Files          18       19       +1     
  Lines         862      906      +44     
==========================================
+ Hits          803      842      +39     
- Misses         59       64       +5     

Impacted Files	Coverage Δ
R/init.R	9.09% <ø> (ø)
R/tidyverse.R	96.77% <ø> (ø)
R/scale_units.R	88.63% <88.63%> (ø)

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[Enchufa2]

Thanks, @edzer.

And @krlmlr thanks for your reference implementation in pillar. Here's ours, any comments welcome. The only drawback is that both require pillar/units to be attached, not only loaded, for the scales to work. Can you think of any way to make ggplot2 find these scales when the packages are only loaded?

[krlmlr]

Thanks, good catch:

data <- tibble::tibble(
  x = pillar::num((1:10) / 100, fixed_exponent = -3, notation = "eng"),
  y = pillar::num((1:10) / 100, scale = 100, label = "%"),
  z = pillar::num(10^(-5:4), notation = "si")
)
data
#> # A tibble: 10 × 3
#>         x     y     z
#>     <eng>     %  <si>
#>  1  10e-3     1   10µ
#>  2  20e-3     2  100µ
#>  3  30e-3     3    1m
#>  4  40e-3     4   10m
#>  5  50e-3     5  100m
#>  6  60e-3     6    1 
#>  7  70e-3     7   10 
#>  8  80e-3     8  100 
#>  9  90e-3     9    1k
#> 10 100e-3    10   10k

ggplot2::ggplot(data, ggplot2::aes(x, y)) +
  ggplot2::geom_point()

^{Created on 2021-12-28 by the reprex package (v2.0.1)}

I'll try to fix in pillar.

[krlmlr]

This is a current limitation, about to file a ggplot2 issue.

For now, should scale_type() raise a warning if the package is not attached?

[Enchufa2]

This is a current limitation, about to file a ggplot2 issue.

Great, thanks.

For now, should scale_type() raise a warning if the package is not attached?

That's a very good idea.

[Enchufa2]

9ec86ee will do for now. In our case, I used stop because the plot would throw a more confusing error anyway. In your case, a warning would be more appropriate. And the good thing is that scale_type is not called when the scales are explicitly provided, so the error/warning doesn't trigger. Example:

library(ggplot2)
mtcars$consumption <- units::set_units(mtcars$mpg, mi / gallon)
mtcars$power <- units::set_units(mtcars$hp, hp)

ggplot(mtcars) +
  geom_point(aes(power, consumption))
#> Error in scale_type.units(x): Variable of class 'units' found, but 'units' package is not attached.
#>   Please, attach it using 'library(units)' to properly show scales with units.

ggplot(mtcars) +
  geom_point(aes(power, consumption)) +
  units::scale_x_units(unit = "W") +
  units::scale_y_units(unit = "km/l")

library(units)
#> udunits database from /usr/share/udunits/udunits2.xml
ggplot(mtcars) +
  geom_point(aes(power, consumption))

^{Created on 2021-12-28 by the reprex package (v2.0.1)}