ChemoSpec: plot2Loadings – R documentation

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plot2Loadings

Plot PCA Loadings from a Spectra Object Against Each Other

Description

Plots two PCA loadings specified by the user, and labels selected (extreme) points. Typically used to determine which variables (frequencies) are co-varying, although in spectroscopy most peaks are represented by several variables and hence there is a lot of co-varying going on. Also useful to determine which variables are contributing the most to the clustering on a score plot.

Usage

plot2Loadings(spectra, pca, loads = c(1, 2), tol = 0.05, ...)

Arguments

`spectra`	An object of S3 class `Spectra`.
`pca`	An object of class `prcomp`, modified to include a list element called `$method`, a character string describing the pre-processing carried out and the type of PCA performed (it appears on the plot). This is automatically provided if `ChemoSpec` functions `c_pcaSpectra` or `r_pcaSpectra` were used to create `pca`.
`loads`	A vector of two integers specifying which loading vectors to plot.
`tol`	A number describing the fraction of points to be labeled. `tol = 1.0` labels all the points; `tol = 0.05` labels the most extreme 5 percent.
`...`	Other parameters to be passed to the plotting routines.

Value

None. Side effect is a plot.

Author(s)

Bryan A. Hanson, DePauw University.

Examples

data(SrE.IR)
pca <- c_pcaSpectra(SrE.IR)
myt <- expression(bolditalic(Serenoa) ~ bolditalic(repens) ~ bold(IR ~ Spectra))
res <- plot2Loadings(SrE.IR, pca,
  main = myt,
  loads = c(1, 2), tol = 0.001
)

ChemoSpec

Exploratory Chemometrics for Spectroscopy

v5.3.11

GPL-3

Authors

Bryan A. Hanson [aut, cre] (<https://orcid.org/0000-0003-3536-8246>), Mike Bostock [cph, ctb] (author of the d3.js library used by plotSpectraJS, http://d3js.org), Matt Keinsley [ctb] (author of initial AOV-PCA code)

Initial release

2021-03-24