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Compute Ratios Between Channels

Source: R/step_channel_ratio.R
step_measure_channel_ratio.Rd

step_measure_channel_ratio() creates a specification of a recipe step that computes ratios between pairs of measurement channels.

Usage

step_measure_channel_ratio(
  recipe,
  numerator,
  denominator,
  output_prefix = "ratio_",
  epsilon = 1e-10,
  log_transform = FALSE,
  remove_original = FALSE,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("measure_channel_ratio")
)

Arguments

recipe

A recipe object.

numerator

Column name(s) for the numerator channel(s).

denominator

Column name(s) for the denominator channel(s). Must have same length as numerator (paired ratios).

output_prefix

Prefix for output column names. Default is "ratio_".

epsilon

Small value added to denominator to avoid division by zero. Default is 1e-10.

log_transform

Logical. Should the ratio be log-transformed? Default is FALSE.

remove_original

Logical. Should original channel columns be removed? Default is FALSE.

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

Channel ratios are useful in analytical chemistry for:

  • Normalization: UV/RI ratios normalize for concentration variations

  • Identification: Characteristic ratios help identify compounds

  • Quality control: Ratio stability indicates system performance

Output Columns

For each numerator/denominator pair, creates a new measure column named {output_prefix}{numerator}_{denominator} (e.g., "ratio_uv_ri").

Log Transform

When log_transform = TRUE, computes log(numerator / denominator) which can be useful for:

  • Normalizing skewed distributions

  • Converting multiplicative relationships to additive

  • Working with absorbance ratios

Note

Channels must be aligned to the same grid before computing ratios. Use step_measure_channel_align() first if grids differ.

See also

Other measure-channel: step_measure_channel_align(), step_measure_channel_combine()

Examples

library(recipes)
library(tibble)

# Create sample multi-channel data
df <- tibble(
  id = rep(1:3, each = 10),
  time = rep(seq(0, 9, by = 1), 3),
  uv = rnorm(30, 100, 10),
  ri = rnorm(30, 50, 5),
  concentration = rep(c(10, 25, 50), each = 10)
)

# Compute UV/RI ratio
rec <- recipe(concentration ~ ., data = df) |>
  update_role(id, new_role = "id") |>
  step_measure_input_long(uv, location = vars(time)) |>
  step_measure_input_long(ri, location = vars(time)) |>
  step_measure_channel_ratio(numerator = "uv", denominator = "ri")