showLabels
Utility Functions to Identify and Mark Extreme Points in a 2D Plot.
This function is called by several graphical functions in the car
package to mark extreme points in a 2D plot. Although the user is unlikely
to call this function directly, the documentation below applies to all
these other functions.
- Keywords
- utilities
Usage
showLabels(x, y, labels=NULL, id.method="identify",
id.n = length(x), id.cex=1, id.col=palette()[1], ...)
Arguments
- x
- Plotted horizontal coordinates.
- y
- Plotted vertical coordinates.
- labels
- Plotting labels. If
NULL
, case numbers will be used. If labels are long, thesubstr
orabbreviate
function can be used to shorten them. - id.method
- How points are to be identified. See Details below.
- id.n
- Number of points to be identified. If set to zero, no points are identified.
- id.cex
- Controls the size of the plotted labels. The default is
1
. - id.col
- Controls the color of the plotted labels.
- ...
- additional arguments passed to
identify
or totext
.
Details
The argument id.method
determine how the points
to be identified are selected. For the default value of id.method="identify"
,
the identify
function is used to identify points
interactively using the mouse. Up to id.n
points can be identified,
so if id.n=0
, which is the default in many functions in the car
package, then no point identification is done.
Automatic point identification can be done depending on the value of the
argument id.method
.
id.method = "x"
select points according to their value ofabs(x - mean(x))
id.method = "y"
select points according to their value ofabs(y - mean(y))
id.method = "mahal"
Treat(x, y)
as if it were a bivariate sample, and select cases according to their Mahalanobis distance from(mean(x), mean(y))
id.method
can be a vector of the same length asx
consisting of values to determine the points to be labeled. For example, for a linear modelm
, settingid.method=cooks.distance(m), id.n=4
will label the points corresponding to the four largest values of Cook's distance, orid.method = abs(residuals(m, type="pearson")), id.n=2
would label the two observations corresponding to the largest absolute Pearson residuals.id.method
can be a vector of case numbers or case-labels, in which case those cases will be labeled, as long asid.n
is greater than zero.
showLabels
, the id.method
argument can be list, so, for
example id.method=list("x", "y")
would label according to the horizontal
and vertical axes variables.
Finally, if the axes in the graph are logged, the function uses logged-variables
where appropriate.
Value
- A utility function used for its side-effect of drawing labels on a plot.
Although intended for use with other functions in the
car
package, this function can be used directly.
References
Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage. Weisberg, S. (2005) Applied Linear Regression, Third Edition, Wiley.
See Also
Examples
plot(income ~ education, Prestige)
with(Prestige, showLabels(education, income,
labels = rownames(Prestige), id.method=list("x", "y"), id.n=3))
m <- lm(income ~ education, Prestige)
plot(income ~ education, Prestige)
abline(m)
with(Prestige, showLabels(education, income,
labels=rownames(Prestige), id.method=abs(residuals(m)), id.n=4))