Compute Ratio to Reference Spectrum

step_measure_ratio_reference() creates a specification of a recipe step that computes the ratio of each spectrum to a reference, optionally with blank subtraction.

Usage

step_measure_ratio_reference(
  recipe,
  reference,
  blank = NULL,
  measures = NULL,
  role = NA,
  trained = FALSE,
  learned_ref = NULL,
  learned_blank = NULL,
  skip = FALSE,
  id = recipes::rand_id("measure_ratio_reference")
)

Arguments

recipe

A recipe object. The step will be added to the sequence of operations for this recipe.

reference

A required external reference spectrum. Can be:

• A measure_tbl object with location and value columns

• A numeric vector (must match the number of locations in data)

• A data.frame with location and value columns (will be interpolated)

blank

An optional blank spectrum to subtract from both sample and reference before computing the ratio. Same format options as reference.

measures

An optional character vector of measure column names to process. If NULL (the default), all measure columns (columns with class measure_list) will be processed.

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.

learned_ref

A named list containing the validated reference values for each measure column. This is NULL until the step is trained.

learned_blank

A named list containing the learned blank values for each measure column. This is NULL until the step is trained.

skip

A logical. Should the step be skipped when the recipe is baked?

id

A character string that is unique to this step to identify it.

Value

An updated version of recipe with the new step added.

Details

This step computes a ratio relative to a reference spectrum:

• Without blank: result = sample / reference

• With blank: result = (sample - blank) / (reference - blank)

This is useful for computing relative measurements, such as absorbance from transmittance when you have both sample and reference scans.

See also

step_measure_subtract_blank() for simple blank subtraction

Other measure-preprocessing: step_measure_absorbance(), step_measure_calibrate_x(), step_measure_calibrate_y(), step_measure_derivative(), step_measure_derivative_gap(), step_measure_emsc(), step_measure_kubelka_munk(), step_measure_log(), step_measure_map(), step_measure_msc(), step_measure_normalize_istd(), step_measure_osc(), step_measure_snv(), step_measure_subtract_blank(), step_measure_subtract_reference(), step_measure_transmittance()

Examples

library(recipes)

# Create reference and blank spectra
ref_spectrum <- rep(1.0, 100)
blank_spectrum <- rep(0.05, 100)

rec <- recipe(water + fat + protein ~ ., data = meats_long) |>
  update_role(id, new_role = "id") |>
  step_measure_input_long(transmittance, location = vars(channel)) |>
  step_measure_ratio_reference(
    reference = ref_spectrum,
    blank = blank_spectrum
  )