optimizePLS: Function to optimize the preprocessing steps for a PLS model.
In griffithdan/plantspec: NIR Calibration and Spectral Data Management in R

Description Usage Arguments Details Value Author(s) Examples

This function iterates all combinations of preprocessing steps and spectral region subsets, fitting PLS models for each, and ranks the resulting models according to the Root Mean Squared Error of Prediction (or CV for cross validation). This process informs the selection of parameters for fitting PLS models with the function calibrate(). The function also determines the rank (number of latent vectors) that is optimal for each model.

1 2	optimizePLS(component, spectra, training_set = NULL, parallel = FALSE, region_list = NULL, preprocessing_list = NULL, max_comps = 10)

`component`	A vector of y-values. One for each spectrum.
`spectra`	An object of class `spectra.matrix` containing spectra. Rows should be in the same order as the component y-values.
`training_set`	A logical vector of `length(component)` specifying `TRUE` for training/calibration data and `FALSE` for test/validation set data.
`parallel`	Logical. The default is `FALSE`; `TRUE` allows for the parallelization of validation proceedures, using the number of available cores - 1. If `FALSE` the function will not be parallelized.
`region_list`	A list, where each element is a vector of length 2, specifying the range (max/min) of a spectral region to select. Should be in the same units as your spectra (e.g., wavenumbers).
`preprocessing_list`	A list, where each element is either (1) a single character string specifying a preprocessing step or (2) a vector of length 2 specifying a series of preprocessing steps to be applied together. See documentation for `preprocess()` for all available options.
`max_comps`	What is the maximum number of latent vectors to possibly include in the PLS regression. An integer.

By default the spectral regions are defined in wavenumbers as list(c(9400,7500), c(7500,6100), c(6100,5450), c(5450,4600), c(4600,4250)).

Returns an object of class PLSopt. The object is a list containing the optimization results. See the following:

optimization_results - a data.frame containing the RMSEP for each combination of preprocessing and subsetting tested
param_subsets - a list of regions tried
param_preproc - a list of preprecessing steps tried.

Daniel M Griffith