Creates a multi-panel plot of loadings along with a reference spectrum.

plotLoadings(spectra, pca, loads = c(1), ref = 1, ...)



An object of S3 class Spectra().


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.


An integer vector giving the loadings to plot. More than 3 loadings creates a useless plot using the default graphics window.


An integer specifying the reference spectrum to plot, which appears at the bottom of the plot.


Parameters to be passed to the plotting routines. Applies to base graphics only.


The returned value depends on the graphics option selected (see GraphicsOptions()).

  • base: None. Side effect is a plot.

  • ggplot2: The plot is displayed, and a ggplot2 object is returned if the value is assigned. The plot can be modified in the usual ggplot2 manner.

See also

c_pcaSpectra for an example. See plot2Loadings to plot two loadings against each other, and sPlotSpectra for an alternative approach. Additional documentation at


Bryan A. Hanson (DePauw University), Tejasvi Gupta.