Calculate Statistical Moments

step_measure_moments() creates a specification of a recipe step that calculates statistical moments from spectra.

Usage

step_measure_moments(
  recipe,
  moments = c("mean", "sd", "skewness", "kurtosis"),
  weighted = FALSE,
  measures = NULL,
  prefix = "moment_",
  role = "predictor",
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("measure_moments")
)

Arguments

recipe

A recipe object.

moments

Character vector specifying which moments to calculate. Options: "mean", "sd", "skewness", "kurtosis", "entropy". Default is c("mean", "sd", "skewness", "kurtosis").

weighted

Logical. If TRUE, moments are weighted by location values. Default is FALSE.

measures

An optional character vector of measure column names.

prefix

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

role

Role for generated columns. Default is "predictor".

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

This step calculates statistical moments that summarize the distribution of values in each spectrum:

Moment	Description
mean	Mean value of the spectrum
sd	Standard deviation of values
skewness	Asymmetry of the distribution
kurtosis	"Tailedness" of the distribution
entropy	Shannon entropy (requires positive values)

When weighted = TRUE, the location (x-axis) values are used as weights, which can be useful for calculating center of mass or weighted statistics.

See also

Other measure-features: step_measure_bin(), step_measure_integrals(), step_measure_ratios()

Examples

library(recipes)

rec <- recipe(water + fat + protein ~ ., data = meats_long) |>
  update_role(id, new_role = "id") |>
  step_measure_input_long(transmittance, location = vars(channel)) |>
  step_measure_moments(moments = c("mean", "sd", "skewness")) |>
  prep()

bake(rec, new_data = NULL)
#> # A tibble: 215 × 9
#>       id water   fat protein .measures channel     moment_mean moment_sd
#>    <int> <dbl> <dbl>   <dbl>    <meas> <list>            <dbl>     <dbl>
#>  1     1  60.5  22.5    16.7 [100 × 2] <int [100]>        2.97     0.270
#>  2     2  46    40.1    13.5 [100 × 2] <int [100]>        3.24     0.234
#>  3     3  71     8.4    20.5 [100 × 2] <int [100]>        2.82     0.206
#>  4     4  72.8   5.9    20.7 [100 × 2] <int [100]>        3.09     0.238
#>  5     5  58.3  25.5    15.5 [100 × 2] <int [100]>        3.25     0.326
#>  6     6  44    42.7    13.7 [100 × 2] <int [100]>        3.48     0.262
#>  7     7  44    42.7    13.7 [100 × 2] <int [100]>        3.44     0.249
#>  8     8  69.3  10.6    19.3 [100 × 2] <int [100]>        2.87     0.280
#>  9     9  61.4  19.9    17.7 [100 × 2] <int [100]>        3.79     0.329
#> 10    10  61.4  19.9    17.7 [100 × 2] <int [100]>        3.94     0.345
#> # ℹ 205 more rows
#> # ℹ 1 more variable: moment_skewness <dbl>