Logarithmic transformation

step_log() creates a specification of a recipe step that will log transform data.

Usage

step_log(
  recipe,
  ...,
  role = NA,
  trained = FALSE,
  base = exp(1),
  offset = 0,
  columns = NULL,
  skip = FALSE,
  signed = FALSE,
  id = rand_id("log")
)

Arguments

recipe: A recipe object. The step will be added to the sequence of operations for this recipe.
...: One or more selector functions to choose variables for this step. See selections() for more details.
role: Not used by this step since no new variables are created.
trained: A logical to indicate if the quantities for preprocessing have been estimated.
base: A numeric value for the base.
offset: An optional value to add to the data prior to logging (to avoid log(0)).
columns: A character string of the selected variable names. This field is a placeholder and will be populated once prep() is used.
skip: A logical. Should the step be skipped when the recipe is baked by bake()? While all operations are baked when prep() is run, some operations may not be able to be conducted on new data (e.g. processing the outcome variable(s)). Care should be taken when using skip = TRUE as it may affect the computations for subsequent operations.
signed: A logical indicating whether to take the signed log. This is sign(x) * log(abs(x)) when abs(x) => 1 or 0 if abs(x) < 1. If TRUE the offset argument will be ignored.
id: A character string that is unique to this step to identify it.

Value

An updated version of recipe with the new step added to the sequence of any existing operations.

Tidying

When you tidy() this step, a tibble is returned with columns terms, base , and id:

terms: character, the selectors or variables selected
base: numeric, value for the base
id: character, id of this step

Case weights

The underlying operation does not allow for case weights.

Examples

set.seed(313)
examples <- matrix(exp(rnorm(40)), ncol = 2)
examples <- as.data.frame(examples)

rec <- recipe(~ V1 + V2, data = examples)

log_trans <- rec %>%
  step_log(all_numeric_predictors())

log_obj <- prep(log_trans, training = examples)

transformed_te <- bake(log_obj, examples)
plot(examples$V1, transformed_te$V1)


tidy(log_trans, number = 1)
#> # A tibble: 1 × 3
#>   terms                     base id       
#>   <chr>                    <dbl> <chr>    
#> 1 all_numeric_predictors()  2.72 log_IhS7o
tidy(log_obj, number = 1)
#> # A tibble: 2 × 3
#>   terms  base id       
#>   <chr> <dbl> <chr>    
#> 1 V1     2.72 log_IhS7o
#> 2 V2     2.72 log_IhS7o

# using the signed argument with negative values

examples2 <- matrix(rnorm(40, sd = 5), ncol = 2)
examples2 <- as.data.frame(examples2)

recipe(~ V1 + V2, data = examples2) %>%
  step_log(all_numeric_predictors()) %>%
  prep(training = examples2) %>%
  bake(examples2)
#> Warning: NaNs produced
#> Warning: NaNs produced
#> Warning: NaNs produced
#> Warning: NaNs produced
#> # A tibble: 20 × 2
#>         V1       V2
#>      <dbl>    <dbl>
#>  1  -0.209 NaN     
#>  2   1.71  NaN     
#>  3   1.12    1.06  
#>  4   1.65    1.19  
#>  5 NaN       2.18  
#>  6   1.15    1.08  
#>  7 NaN       0.555 
#>  8   0.102 NaN     
#>  9   0.670   1.37  
#> 10 NaN       1.02  
#> 11 NaN     NaN     
#> 12 NaN     NaN     
#> 13 NaN     NaN     
#> 14   1.25   -0.0880
#> 15   2.21    0.774 
#> 16 NaN     NaN     
#> 17 NaN       2.49  
#> 18 NaN       1.47  
#> 19 NaN     NaN     
#> 20 NaN     NaN     

recipe(~ V1 + V2, data = examples2) %>%
  step_log(all_numeric_predictors(), signed = TRUE) %>%
  prep(training = examples2) %>%
  bake(examples2)
#> # A tibble: 20 × 2
#>        V1      V2
#>     <dbl>   <dbl>
#>  1  0     -1.24  
#>  2  1.71  -1.81  
#>  3  1.12   1.06  
#>  4  1.65   1.19  
#>  5 -1.63   2.18  
#>  6  1.15   1.08  
#>  7 -0.604  0.555 
#>  8  0.102 -0.565 
#>  9  0.670  1.37  
#> 10 -2.65   1.02  
#> 11 -1.34  -1.04  
#> 12 -2.06  -1.51  
#> 13 -0.613 -1.75  
#> 14  1.25   0     
#> 15  2.21   0.774 
#> 16 -1.90  -0.0814
#> 17 -0.762  2.49  
#> 18 -1.40   1.47  
#> 19 -1.22  -0.825 
#> 20 -1.20  -2.27