Return function of transformed response variables

This functions checks whether any transformation, such as log- or exp-transforming, was applied to the response variable (dependent variable) in a regression formula, and returns the related function that was used for transformation. See find_transformation() for an overview of supported transformations that are detected.

Usage

get_transformation(x, include_all = FALSE, verbose = TRUE)

Arguments

x

A regression model or a character string of the formulation of the (response) variable.

include_all

Logical, if TRUE, does not only check the response variable, but all model terms.

verbose

Logical, if TRUE, prints a warning if the transformation could not be determined.

Value

A list of two functions: $transformation, the function that was used to transform the response variable; $inverse, the inverse-function of $transformation (can be used for "back-transformation"). If no transformation was applied, both list-elements $transformation and $inverse just return function(x) x. If transformation is unknown, NULL is returned.

Examples

# identity, no transformation
model <- lm(Sepal.Length ~ Species, data = iris)
get_transformation(model)
#> $transformation
#> function (x) 
#> x
#> <bytecode: 0x55c3d416ab90>
#> <environment: 0x55c3d4156a38>
#> 
#> $inverse
#> function (x) 
#> x
#> <bytecode: 0x55c3d416ab90>
#> <environment: 0x55c3d4156a38>
#> 

# log-transformation
model <- lm(log(Sepal.Length) ~ Species, data = iris)
get_transformation(model)
#> $transformation
#> function (x, base = exp(1))  .Primitive("log")
#> 
#> $inverse
#> function (x)  .Primitive("exp")
#> 

# log-function
get_transformation(model)$transformation(0.3)
#> [1] -1.203973
log(0.3)
#> [1] -1.203973

# inverse function is exp()
get_transformation(model)$inverse(0.3)
#> [1] 1.349859
exp(0.3)
#> [1] 1.349859

# get transformations for all model terms
model <- lm(mpg ~ log(wt) + I(gear^2) + exp(am), data = mtcars)
get_transformation(model, include_all = TRUE)
#> $response
#> $response$mpg
#> $response$mpg$transformation
#> function (x) 
#> x
#> <bytecode: 0x55c3d416ab90>
#> <environment: 0x55c3d2dc8868>
#> 
#> $response$mpg$inverse
#> function (x) 
#> x
#> <bytecode: 0x55c3d416ab90>
#> <environment: 0x55c3d2dc8868>
#> 
#> 
#> 
#> $conditional
#> $conditional$wt
#> $conditional$wt$transformation
#> function (x, base = exp(1))  .Primitive("log")
#> 
#> $conditional$wt$inverse
#> function (x)  .Primitive("exp")
#> 
#> 
#> $conditional$gear
#> $conditional$gear$transformation
#> function (x) 
#> x^2
#> <environment: 0x55c3d2cb90d8>
#> 
#> $conditional$gear$inverse
#> function (x) 
#> x^(2^-1)
#> <environment: 0x55c3d2cb90d8>
#> 
#> 
#> $conditional$am
#> $conditional$am$transformation
#> function (x)  .Primitive("exp")
#> 
#> $conditional$am$inverse
#> function (x, base = exp(1))  .Primitive("log")
#> 
#> 
#>