Plots of Scores, Loadings and Correlation Loadings

Functions to make scatter plots of scores or correlation loadings, and scatter or line plots of loadings.

scoreplot(object, ...)
# S3 method for default
scoreplot(object, comps = 1:2, labels, identify = FALSE, type = "p",
          xlab, ylab, ...)
# S3 method for scores
plot(x, ...)

loadingplot(object, ...)
# S3 method for default
loadingplot(object, comps = 1:2, scatter = FALSE, labels,
            identify = FALSE, type, lty, lwd = NULL, pch, cex = NULL,
            col, legendpos, xlab, ylab, pretty.xlabels = TRUE, xlim, ...)
# S3 method for loadings
plot(x, ...)

corrplot(object, comps = 1:2, labels, plotx = TRUE, ploty = FALSE,
         radii = c(sqrt(1/2), 1), identify = FALSE, type = "p",
         xlab, ylab, col, ...)

Arguments

object	an R object. The fitted model.
comps	integer vector. The components to plot.
scatter	logical. Whether the loadings should be plotted as a scatter instead of as lines.
labels	optional. Alternative plot labels or \(x\) axis labels. See Details.
plotx	locical. Whether to plot the \(X\) correlation loadings. Defaults to `TRUE`.
ploty	locical. Whether to plot the \(Y\) correlation loadings. Defaults to `FALSE`.
radii	numeric vector, giving the radii of the circles drawn in `corrplot`. The default radii represent 50% and 100% explained variance of the \(X\) variables by the chosen components.
identify	logical. Whether to use `identify` to interactively identify points. See below.
type	character. What type of plot to make. Defaults to `"p"` (points) for scatter plots and `"l"` (lines) for line plots. See `plot` for a complete list of types (not all types are possible/meaningful for all plots).
lty	vector of line types (recycled as neccessary). Line types can be specified as integers or character strings (see `par` for the details).
lwd	vector of positive numbers (recycled as neccessary), giving the width of the lines.
pch	plot character. A character string or a vector of single characters or integers (recycled as neccessary). See `points` for all alternatives.
cex	numeric vector of character expansion sizes (recycled as neccessary) for the plotted symbols.
col	character or integer vector of colors for plotted lines and symbols (recycled as neccessary). See `par` for the details.
legendpos	Legend position. Optional. Ignored if `scatter` is `TRUE`. If present, a legend is drawn at the given position. The position can be specified symbolically (e.g., `legendpos = "topright"`). This requires R >= 2.1.0. Alternatively, the position can be specified explicitly (`legendpos = t(c(x,y))`) or interactively (`legendpos = locator()`).
xlab,ylab	titles for \(x\) and \(y\) axes. Typically character strings, but can be expressions or lists. See `title` for details.
pretty.xlabels	logical. If `TRUE`, `loadingplot` tries to plot the \(x\) labels more nicely. See Details.
xlim	optional vector of length two, with the \(x\) limits of the plot.
x	a `scores` or `loadings` object. The scores or loadings to plot.
...	further arguments sent to the underlying plot function(s).

Details

plot.scores is simply a wrapper calling scoreplot, passing all arguments. Similarly for plot.loadings.

scoreplot is generic, currently with a default method that works for matrices and any object for which scores returns a matrix. The default scoreplot method makes one or more scatter plots of the scores, depending on how many components are selected. If one or two components are selected, and identify is TRUE, the function identify is used to interactively identify points.

Also loadingplot is generic, with a default method that works for matrices and any object where loadings returns a matrix. If scatter is TRUE, the default method works exactly like the default scoreplot method. Otherwise, it makes a lineplot of the selected loading vectors, and if identify is TRUE, uses identify to interactively identify points. Also, if legendpos is given, a legend is drawn at the position indicated.

corrplot works exactly like the default scoreplot method, except that at least two components must be selected. The “correlation loadings”, i.e. the correlations between each variable and the selected components (see References), are plotted as pairwise scatter plots, with concentric circles of radii given by radii. Each point corresponds to a variable. The squared distance between the point and origin equals the fraction of the variance of the variable explained by the components in the panel. The default radii corresponds to 50% and 100% explained variance. By default, only the correlation loadings of the \(X\) variables are plotted, but if ploty is TRUE, also the \(Y\) correlation loadings are plotted.

scoreplot, loadingplot and corrplot can also be called through the plot method for mvr objects, by specifying plottype as "scores", "loadings" or "correlation", respectively. See plot.mvr.

The argument labels can be a vector of labels or one of "names" and "numbers".

If a scatter plot is produced (i.e., scoreplot, corrplot, or loadingplot with scatter = TRUE), the labels are used instead of plot symbols for the points plotted. If labels is "names" or "numbers", the row names or row numbers of the matrix (scores, loadings or correlation loadings) are used.

If a line plot is produced (i.e., loadingplot), the labels are used as \(x\) axis labels. If labels is "names" or "numbers", the variable names are used as labels, the difference being that with "numbers", the variable names are converted to numbers, if possible. Variable names of the forms "number" or "number text" (where the space is optional), are handled.

The argument pretty.xlabels is only used when labels is specified for a line plot. If TRUE (default), the code tries to use a ‘pretty’ selection of labels. If labels is "numbers", it also uses the numerical values of the labels for horisontal spacing. If one has excluded parts of the spectral region, one might therefore want to use pretty.xlabels = FALSE.

Value

The functions return whatever the underlying plot function (or identify) returns.

References

Martens, H., Martens, M. (2000) Modified Jack-knife Estimation of Parameter Uncertainty in Bilinear Modelling by Partial Least Squares Regression (PLSR). Food Quality and Preference, 11(1--2), 5--16.

Note

legend has many options. If you want greater control over the appearance of the legend, omit the legendpos argument and call legend manually.

Graphical parametres (such as pch and cex) can also be used with scoreplot and corrplot. They are not listed in the argument list simply because they are not handled specifically in the function (unlike in loadingplot), but passed directly to the underlying plot functions by ....

Tip: If the labels specified with labels are too long, they get clipped at the border of the plot region. This can be avoided by supplying the graphical parameter xpd = TRUE in the plot call.

The handling of labels and pretty.xlabels in coefplot is experimental.

Examples

data(yarn)
mod <- plsr(density ~ NIR, ncomp = 10, data = yarn)
## These three are equivalent:
if (FALSE) {
scoreplot(mod, comps = 1:5)
plot(scores(mod), comps = 1:5)
plot(mod, plottype = "scores", comps = 1:5)

loadingplot(mod, comps = 1:5)
loadingplot(mod, comps = 1:5, legendpos = "topright") # With legend
loadingplot(mod, comps = 1:5, scatter = TRUE) # Plot as scatterplots

corrplot(mod, comps = 1:2)
corrplot(mod, comps = 1:3)
}