Convert ordinal factors to numeric scores

step_ordinalscore() creates a specification of a recipe step that will convert ordinal factor variables into numeric scores.

Usage

step_ordinalscore(
  recipe,
  ...,
  role = NA,
  trained = FALSE,
  columns = NULL,
  convert = as.numeric,
  skip = FALSE,
  id = rand_id("ordinalscore")
)

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.
columns: A character string of the selected variable names. This field is a placeholder and will be populated once prep() is used.
convert: A function that takes an ordinal factor vector as an input and outputs a single numeric variable.
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.
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.

Details

Dummy variables from ordered factors with C levels will create polynomial basis functions with C-1 terms. As an alternative, this step can be used to translate the ordered levels into a single numeric vector of values that represent (subjective) scores. By default, the translation uses a linear scale (1, 2, 3, ... C) but custom score functions can also be used (see the example below).

Tidying

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

terms: character, the selectors or variables selected
id: character, id of this step

Case weights

The underlying operation does not allow for case weights.

Examples

fail_lvls <- c("meh", "annoying", "really_bad")

ord_data <-
  data.frame(
    item = c("paperclip", "twitter", "airbag"),
    fail_severity = factor(fail_lvls,
      levels = fail_lvls,
      ordered = TRUE
    )
  )

model.matrix(~fail_severity, data = ord_data)
#>   (Intercept) fail_severity.L fail_severity.Q
#> 1           1   -7.071068e-01       0.4082483
#> 2           1   -7.850462e-17      -0.8164966
#> 3           1    7.071068e-01       0.4082483
#> attr(,"assign")
#> [1] 0 1 1
#> attr(,"contrasts")
#> attr(,"contrasts")$fail_severity
#> [1] "contr.poly"
#> 

linear_values <- recipe(~ item + fail_severity, data = ord_data) %>%
  step_dummy(item) %>%
  step_ordinalscore(fail_severity)

linear_values <- prep(linear_values, training = ord_data)

bake(linear_values, new_data = NULL)
#> # A tibble: 3 × 3
#>   fail_severity item_paperclip item_twitter
#>           <int>          <dbl>        <dbl>
#> 1             1              1            0
#> 2             2              0            1
#> 3             3              0            0

custom <- function(x) {
  new_values <- c(1, 3, 7)
  new_values[as.numeric(x)]
}

nonlin_scores <- recipe(~ item + fail_severity, data = ord_data) %>%
  step_dummy(item) %>%
  step_ordinalscore(fail_severity, convert = custom)

tidy(nonlin_scores, number = 2)
#> # A tibble: 1 × 2
#>   terms         id                
#>   <chr>         <chr>             
#> 1 fail_severity ordinalscore_eIAmG

nonlin_scores <- prep(nonlin_scores, training = ord_data)

bake(nonlin_scores, new_data = NULL)
#> # A tibble: 3 × 3
#>   fail_severity item_paperclip item_twitter
#>           <int>          <dbl>        <dbl>
#> 1             1              1            0
#> 2             3              0            1
#> 3             7              0            0

tidy(nonlin_scores, number = 2)
#> # A tibble: 1 × 2
#>   terms         id                
#>   <chr>         <chr>             
#> 1 fail_severity ordinalscore_eIAmG