step_gap_derivative() creates a specification of a recipe step that
computes the gap-segment (Norris-Williams) derivative of the spectra with
gap_derivative().
Usage
step_gap_derivative(
recipe,
...,
derivative = 1,
gap = 5,
segment = 3,
segments = TRUE,
role = NA,
trained = FALSE,
columns = NULL,
skip = FALSE,
id = recipes::rand_id("gap_derivative")
)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 the predictors (for example, the spectral channels). See
recipes::selections().- derivative
The derivative: 1 (default) or 2.
- gap
The number of channels between two segments, an odd number. Default is 5.
- segment
The number of channels averaged in each segment, an odd number. Default is 3.
- segments
A logical: filter the segments between gaps of the wavelength axis separately (
TRUE, default). Needs wavelengths as names.- role
Not used by this step, since no new variables are created.
- trained
A logical indicating whether the step has been trained.
- columns
The names of the selected columns, stored once the step has been trained.
- skip
A logical. Should the step be skipped when the recipe is baked by
recipes::bake()? Keep the defaultFALSE, so that new data are corrected with the same filter as the training data.- id
A character string that is unique to this step.
Details
The selected columns form one spectrum per row, and are replaced by their
derivative. Nothing is estimated from the training data. The derivative,
gap and segment can be tuned with tune::tune() (dials parameters
savgol_derivative(), with values 1 and 2, and window_size()); an even
gap or segment, as a tuning grid may propose, is increased to the next
odd number. tidy() returns the terms,
derivative, gap, segment and id.
Examples
if (rlang::is_installed("recipes")) {
data(forageLIBS)
rec <- recipes::recipe(K ~ ., data = forageLIBS[-c(1:10, 12:14)]) |>
step_gap_derivative(recipes::all_predictors(), gap = 5, segment = 3) |>
recipes::prep()
recipes::tidy(rec, number = 1)
}
#> # A tibble: 7,152 × 5
#> terms derivative gap segment id
#> <chr> <dbl> <dbl> <dbl> <chr>
#> 1 199.3771616 1 5 3 gap_derivative_yTKKH
#> 2 199.4644141 1 5 3 gap_derivative_yTKKH
#> 3 199.5516666 1 5 3 gap_derivative_yTKKH
#> 4 199.6389192 1 5 3 gap_derivative_yTKKH
#> 5 199.7261717 1 5 3 gap_derivative_yTKKH
#> 6 199.8134242 1 5 3 gap_derivative_yTKKH
#> 7 199.9006767 1 5 3 gap_derivative_yTKKH
#> 8 199.9879292 1 5 3 gap_derivative_yTKKH
#> 9 200.0751817 1 5 3 gap_derivative_yTKKH
#> 10 200.1624343 1 5 3 gap_derivative_yTKKH
#> # ℹ 7,142 more rows