| showLabels {car} | R Documentation |
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.
showLabels(x, y, labels=NULL, id.method="identify",
id.n = length(x), id.cex=1, id.col=palette()[1], ...)
x |
Plotted horizontal coordinates. |
y |
Plotted vertical coordinates. |
labels |
Plotting labels. If |
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 |
id.col |
Controls the color of the plotted labels. |
... |
additional arguments passed to |
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 of abs(x - mean(x))
id.method = "y" select points according to their value of abs(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 as x consisting of
values to determine the points to be labeled. For example, for a linear model
m, setting id.method=cooks.distance(m), id.n=4 will label the
points corresponding to the four largest values of Cook's distance, or
id.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 as id.n is greater than zero.
With 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.
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.
John Fox jfox@mcmaster.ca, Sanford Weisberg sandy@umn.edu
Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.
Weisberg, S. (2005) Applied Linear Regression, Third Edition, Wiley.
avPlots, residualPlots,
crPlots, leveragePlots
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))