plot.cca {vegan}R Documentation

Plot or Extract Results of Constrained Correspondence Analysis or Redundancy Analysis

Description

Functions to plot or extract results of constrained correspondence analysis (cca), redundancy analysis (rda) or constrained analysis of principal coordinates (capscale).

Usage

## S3 method for class 'cca':
plot(x, choices = c(1, 2), display = c("sp", "wa", "cn"),
         scaling = 2, type, xlim, ylim, const, ...)
## S3 method for class 'cca':
text(x, display = "sites", labels, choices = c(1, 2), scaling = 2,
    arrow.mul, head.arrow = 0.05, select, const, ...)
## S3 method for class 'cca':
points(x, display = "sites", choices = c(1, 2), scaling = 2,
    arrow.mul, head.arrow = 0.05, select, const, ...)
## S3 method for class 'cca':
scores(x, choices=c(1,2), display=c("sp","wa","cn"), scaling=2, ...)
## S3 method for class 'rda':
scores(x, choices=c(1,2), display=c("sp","wa","cn"), scaling=2, 
    const, ...)
## S3 method for class 'cca':
summary(object, scaling = 2, axes = 6, display = c("sp", "wa", 
    "lc", "bp", "cn"), digits = max(3, getOption("digits") - 3), ...)
## S3 method for class 'summary.cca':
print(x, digits = x$digits, head = NA, tail = head, ...)
## S3 method for class 'summary.cca':
head(x, n = 6, tail = 0, ...)
## S3 method for class 'summary.cca':
tail(x, n = 6, head = 0, ...)

Arguments

x, object A cca result object.
choices Axes shown.
display Scores shown. These must some of the alternatives species or sp for species scores, sites or wa for site scores, lc for linear constraints or ``LC scores'', or bp for biplot arrows or cn for centroids of factor constraints instead of an arrow.
scaling Scaling for species and site scores. Either species (2) or site (1) scores are scaled by eigenvalues, and the other set of scores is left unscaled, or with 3 both are scaled symmetrically by square root of eigenvalues. Corresponding negative values can be used in cca to additionally multiply results with sqrt(1/(1-λ)). This scaling is know as Hill scaling (although it has nothing to do with Hill's rescaling of decorana). With corresponding negative values inrda, species scores are divided by standard deviation of each species and multiplied with an equalizing constant. Unscaled raw scores stored in the result can be accessed with scaling = 0.
type Type of plot: partial match to text for text labels, points for points, and none for setting frames only. If omitted, text is selected for smaller data sets, and points for larger.
xlim, ylim the x and y limits (min,max) of the plot.
labels Optional text to be used instead of row names.
arrow.mul Factor to expand arrows in the graph. Arrows will be scaled automatically to fit the graph if this is missing.
head.arrow Default length of arrow heads.
select Items to be displayed. This can either be a logical vector which is TRUE for displayed items or a vector of indices of displayed items.
const General scaling constant to rda scores. The default is to use constant to give biplot scores, or scores that approximate original data.
axes Number of axes in summaries.
digits Number of digits in output.
n, head, tail Number of rows printed from the head and tail of species and site scores. Default NA prints all.
... Parameters passed to other functions.

Details

Same plot function will be used for cca and rda. This produces a quick, standard plot with current scaling.

The plot function sets colours (col), plotting characters (pch) and character sizes (cex) to certain standard values. For a fuller control of produced plot, it is best to call plot with type="none" first, and then add each plotting item separately using text.cca or points.cca functions. These use the default settings of standard text and points functions and accept all their parameters, allowing a full user control of produced plots.

Environmental variables receive a special treatment. With display="bp", arrows will be drawn. These are labelled with text and unlabelled with points. The basic plot function uses a simple (but not very clever) heuristics for adjusting arrow lengths to plots, but the user can give the expansion factor in mul.arrow. With display="cn" the centroids of levels of factor variables are displayed (these are available only if there were factors and a formula interface was used in cca or rda). With this option continuous variables still are presented as arrows and ordered factors as arrows and centroids.

If you want to have still a better control of plots, it is better to produce them using primitive plot commands. Function scores helps in extracting the needed components with the selected scaling.

Function summary lists all scores and the output can be very long. You can suppress scores by setting axes = 0 or display = NA or display = NULL. You can display some first or last (or both) rows of scores by using head or tail or explicit print command for the summary.

Palmer (1993) suggested using linear constraints (``LC scores'') in ordination diagrams, because these gave better results in simulations and site scores (``WA scores'') are a step from constrained to unconstrained analysis. However, McCune (1997) showed that noisy environmental variables (and all environmental measurements are noisy) destroy ``LC scores'' whereas ``WA scores'' were little affected. Therefore the plot function uses site scores (``WA scores'') as the default. This is consistent with the usage in statistics and other functions in R (lda, cancor).

Value

The plot function returns invisibly a plotting structure which can be used by function identify.ordiplot to identify the points or other functions in the ordiplot family.

Note

Package ade4 has function cca which returns constrained correspondence analysis of the same class as the vegan function. If you have results of ade4 in your working environment, vegan functions may try to handle them and fail with cryptic error messages. However, there is a simple utility function ade2vegancca which tries to translate ade4 cca results to vegan cca results so that some vegan functions may work partially with ade4 objects (with a warning).

Author(s)

Jari Oksanen

See Also

cca, rda and capscale for getting something to plot, ordiplot for an alternative plotting routine and more support functions, and text, points and arrows for the basic routines.

Examples

data(dune)
data(dune.env)
mod <- cca(dune ~ A1 + Moisture + Management, dune.env)
plot(mod, type="n")
text(mod, dis="cn")
points(mod, pch=21, col="red", bg="yellow", cex=1.2)
text(mod, "species", col="blue", cex=0.8)
## Limited output of 'summary'
head(summary(mod), tail=2)

[Package vegan version 1.16-32 Index]