Align to Reference Spectrum

step_measure_align_reference() creates a specification of a recipe step that aligns spectra to a user-provided reference spectrum using cross-correlation.

Usage

step_measure_align_reference(
  recipe,
  measures = NULL,
  ref_spectrum,
  max_shift = 10L,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("measure_align_reference")
)

Arguments

recipe

A recipe object.

measures

An optional character vector of measure column names.

ref_spectrum

A numeric vector containing the reference spectrum. Must have the same length as the measurement spectra.

max_shift

Maximum shift (in points) to consider. Default is 10.

role

Not used.

trained

Logical indicating if the step has been trained.

skip

Logical. Should the step be skipped when baking?

id

Unique step identifier.

Value

An updated recipe with the new step added.

Details

Similar to step_measure_align_shift(), but uses an externally provided reference spectrum instead of computing one from training data. This is useful when you have a known standard or calibration spectrum.

See also

Other measure-align: step_measure_align_cow(), step_measure_align_dtw(), step_measure_align_ptw(), step_measure_align_shift()

Examples

library(recipes)

# Create a reference spectrum (in practice, this would be from calibration)
ref <- rep(1, 100)  # placeholder

# Note: This example would need matching spectrum lengths to work
if (FALSE) { # \dontrun{
rec <- recipe(water + fat + protein ~ ., data = meats_long) |>
  update_role(id, new_role = "id") |>
  step_measure_input_long(transmittance, location = vars(channel)) |>
  step_measure_align_reference(ref_spectrum = ref) |>
  prep()
} # }