find_transformation incorrectly detects power transformations

[strengejacke]

Fixes #812

[codecov]

Codecov Report

Merging #813 (ca31179) into main (6e78a4b) will decrease coverage by 0.04%.
Report is 16 commits behind head on main.
The diff coverage is 50.46%.

❗ Current head ca31179 differs from pull request most recent head f6b6940. Consider uploading reports for the commit f6b6940 to get more accurate results

@@            Coverage Diff             @@
##             main     #813      +/-   ##
==========================================
- Coverage   54.57%   54.53%   -0.04%     
==========================================
  Files         124      124              
  Lines       15249    15291      +42     
==========================================
+ Hits         8322     8339      +17     
- Misses       6927     6952      +25     

Files	Coverage Δ
R/all_equal_models.R	96.42% <ø> (ø)
R/check_if_installed.R	73.97% <ø> (ø)
R/clean_names.R	81.39% <ø> (ø)
R/clean_parameters.R	63.68% <ø> (ø)
R/find_interactions.R	88.46% <ø> (ø)
R/find_offset.R	100.00% <ø> (ø)
R/find_parameter_zi.R	28.20% <ø> (ø)
R/find_parameters_gam.R	83.09% <ø> (ø)
R/find_parameters_mfx.R	0.00% <ø> (ø)
R/find_parameters_other.R	22.72% <ø> (ø)
... and 68 more

[bwiernik]

The regex should also accommodate:

1. Decimal exponents
2. Using ** instead of ^

[strengejacke]

Should work.

@bwiernik @bbolker is it even possible to return the power as function? See:

insight/R/get_transformation.R

Line 61 in b87c1c3

} else if (transform_fun == "power") {

Currently, get_transformation() for power returns:

list(transformation = function(x) x^2, inverse = sqrt)

[bwiernik]

list(
  transformation = function(x, power) x^power, 
  inverse = function(x, power) x^(1/power)
)