ordihull: Display Groups or Factor Levels in Ordination Diagrams

In vegan: Community Ecology Package

Description

Functions to add convex hulls, ‘spider’ graphs, ellipses or cluster dendrogram to ordination diagrams. The ordination diagrams can be produced by vegan plot.cca, plot.decorana or ordiplot.

Usage

ordihull(ord, groups, display = "sites", draw = c("lines","polygon", "none"),
         col = NULL, alpha = 127, show.groups, label = FALSE,  ...)
ordiellipse(ord, groups, display="sites", kind = c("sd","se"), conf,
         draw = c("lines","polygon", "none"), w = weights(ord, display),
         col = NULL, alpha = 127, show.groups, label = FALSE, ...)
ordispider(ord, groups, display="sites", w = weights(ord, display),
	 spiders = c("centroid", "median"),  show.groups, 
         label = FALSE, ...)
ordicluster(ord, cluster, prune = 0, display = "sites",
         w = weights(ord, display), ...)
## S3 method for class 'ordihull'
summary(object, ...)
## S3 method for class 'ordiellipse'
summary(object, ...)
ordiareatest(ord, groups, area = c("hull", "ellipse"), permutations = 999,
         parallel = getOption("mc.cores"), ...)

Arguments

ord	An ordination object or an ordiplot object.
groups	Factor giving the groups for which the graphical item is drawn.
display	Item to displayed.
draw	Use either lines or polygon to draw the lines. Graphical parameters are passed to both. The main difference is that polygons may be filled and non-transparent. With none nothing is drawn, but the function returns the invisible plotting data.
col	Colour of hull or ellipse lines (if draw = "lines") or their fills (if draw = "polygon") in ordihull and ordiellipse. When draw = "polygon", the colour of bordering lines can be set with argument border of the polygon function. For other functions the effect depends on the underlining functions this argument is passed to.
alpha	Transparency of the fill colour with draw = "polygon" in ordihull and ordiellipse. The argument takes precedence over possible transparency definitions of the colour. The value must be in range 0...255, and low values are more transparent. Transparency is not available in all graphics devices or file formats.
show.groups	Show only given groups. This can be a vector, or TRUE if you want to show items for which condition is TRUE. This argument makes it possible to use different colours and line types for groups. The default is to show all groups.
label	Label the groups by their names in the centroid of the object. ordiellipse and ordihull use standard text, and others use ordilabel.
w	Weights used to find the average within group. Weights are used automatically for cca and decorana results, unless undone by the user. w=NULL sets equal weights to all points.
kind	Whether standard deviations of points (sd) or standard deviations of their (weighted) averages (se) are used.
conf	Confidence limit for ellipses, e.g. 0.95. If given, the corresponding sd or se is multiplied with the corresponding value found from the Chi-squared distribution with 2df.
spiders	Are centres or spider bodies calculated either as centroids (averages) or spatial medians.
cluster	Result of hierarchic cluster analysis, such as hclust or agnes.
prune	Number of upper level hierarchies removed from the dendrogram. If prune >0, dendrogram will be disconnected.
object	A result object from ordihull or ordiellipse. The result is invisible, but it can be saved, and used for summaries (areas etc. of hulls and ellipses).
area	Evaluate the area of convex hulls of ordihull, or of ellipses of ordiellipse.
permutations	a list of control values for the permutations as returned by the function how, or the number of permutations required, or a permutation matrix where each row gives the permuted indices.
parallel	Number of parallel processes or a predefined socket cluster. With parallel = 1 uses ordinary, non-parallel processing. The parallel processing is done with parallel package.
...	Parameters passed to graphical functions or to scores to select axes and scaling etc.

Details

Function ordihull draws lines or polygons for the convex hulls found by function chull encircling the items in the groups.

Function ordiellipse draws lines or polygons for dispersion ellipses using either standard deviation of point scores or standard error of the (weighted) average of scores, and the (weighted) correlation defines the direction of the principal axis of the ellipse. An ellipsoid hull can be drawn with function ellipsoidhull of package cluster.

Function ordihull and ordiellipse return invisibly an object that has a summary method that returns the coordinates of centroids and areas of the hulls or ellipses. Function ordiareatest studies the one-sided hypothesis that these areas are smaller than with randomized groups.

Function ordispider draws a ‘spider’ diagram where each point is connected to the group centroid with segments. Weighted centroids are used in the correspondence analysis methods cca and decorana or if the user gives the weights in the call. If ordispider is called with cca or rda result without groups argument, the function connects each ‘WA’ scores to the corresponding ‘LC’ score. If the argument is a (invisible) ordihull object, the function will connect the points of the hull to their centroid.

Function ordicluster overlays a cluster dendrogram onto ordination. It needs the result from a hierarchic clustering such as hclust or agnes, or other with a similar structure. Function ordicluster connects cluster centroids to each other with line segments. Function uses centroids of all points in the clusters, and is therefore similar to average linkage methods.

Value

Functions ordihull, ordiellipse and ordispider return the invisible plotting structure.

Function ordispider return the coordinates to which each point is connected (centroids or ‘LC’ scores).

Function ordihull returns a list of coordinates of the hulls (which can be extracted with scores), and ordiellipse returns a list of covariance matrices and scales used in drawing the ellipses.

Note

These functions add graphical items to ordination graph: You must draw a graph first. To draw line segments, grids or arrows, see ordisegments, ordigrid andordiarrows.

Author(s)

Jari Oksanen

See Also

The functions pass parameters to basic graphical functions, and you may wish to change the default values in lines, segments and polygon. You can pass parameters to scores as well. Underlying function for ordihull is chull.

Examples

data(dune)
data(dune.env)
mod <- cca(dune ~ Management, dune.env)
attach(dune.env)
## pass non-graphical arguments without warnings
plot(mod, type="n", scaling = 3)
## Catch the invisible result of ordihull...
pl <- ordihull(mod, Management, scaling = 3, label = TRUE)
## ... and find centres and areas of the hulls
summary(pl)
## use ordispider to label and mark the hull
plot(mod, type = "n")
pl <- ordihull(mod, Management, scaling = 3)
ordispider(pl, col="red", lty=3, label = TRUE )
## ordispider to connect WA and LC scores
plot(mod, dis=c("wa","lc"), type="p")
ordispider(mod)
## Other types of plots
plot(mod, type = "p", display="sites")
ordicluster(mod, hclust(vegdist(dune)), prune=3, col = "blue")
plot(mod, type="n", display = "sites")
text(mod, display="sites", labels = as.character(Management))
pl <- ordiellipse(mod, Management, kind="se", conf=0.95, lwd=2, draw = "polygon", 
  col="skyblue", border = "blue")
summary(pl)

Example output

Loading required package: permute
Loading required package: lattice
This is vegan 2.4-3
            BF         HF         NM         SF
CCA1 0.2917476 0.36826105 -1.3505642  0.2762936
CCA2 0.8632208 0.09419919  0.2681515 -0.8139398
Area 0.1951715 0.59943363  1.7398193  1.0144372
            BF        HF          NM         SF
CCA1 0.4312652 0.5583211 -1.87848340  0.5601499
CCA2 1.3273917 0.6373120 -0.05503211 -1.3859924
Area 1.4559842 1.3806668  2.73667419  1.5559135

vegan documentation built on May 2, 2019, 5:51 p.m.