boxplot {graphics}  R Documentation 
Produce boxandwhisker plot(s) of the given (grouped) values.
boxplot(x, ...) ## S3 method for class 'formula': boxplot(formula, data = NULL, ..., subset, na.action = NULL) ## Default S3 method: boxplot(x, ..., range = 1.5, width = NULL, varwidth = FALSE, notch = FALSE, outline = TRUE, names, plot = TRUE, border = par("fg"), col = NULL, log = "", pars = list(boxwex = 0.8, staplewex = 0.5, outwex = 0.5), horizontal = FALSE, add = FALSE, at = NULL)
formula 
a formula, such as y ~ grp , where y is a
numeric vector of data values to be split into groups according to
the grouping variable grp (usually a factor). 
data 
a data.frame (or list) from which the variables in
formula should be taken. 
subset 
an optional vector specifying a subset of observations to be used for plotting. 
na.action 
a function which indicates what should happen
when the data contain NA s. The default is to ignore missing
values in either the response or the group. 
x 
for specifying data from which the boxplots are to be
produced. Either a numeric vector, or a single list containing such
vectors. Additional unnamed arguments specify further data
as separate vectors (each corresponding to a component boxplot).
NA s are allowed in the data. 
... 
For the formula method, arguments to the
default method and graphical parameters.
For the default method, unnamed arguments are additional data vectors (unless x is a list when they are ignored),
and named arguments are graphical parameters in addition to the ones
given by argument pars .

range 
this determines how far the plot whiskers extend out
from the box. If range is positive, the whiskers extend
to the most extreme data point which is no more than
range times the interquartile range from the box. A value
of zero causes the whiskers to extend to the data extremes. 
width 
a vector giving the relative widths of the boxes making up the plot. 
varwidth 
if varwidth is TRUE , the boxes are
drawn with widths proportional to the squareroots of the number
of observations in the groups. 
notch 
if notch is TRUE , a notch is drawn in
each side of the boxes. If the notches of two plots do not
overlap this is ‘strong evidence’ that the two medians differ
(Chambers et al., 1983, p. 62). See boxplot.stats
for the calculations used. 
outline 
if outline is not true, the outliers are
not drawn (as points whereas S+ uses lines). 
names 
group labels which will be printed under each boxplot. 
boxwex 
a scale factor to be applied to all boxes. When there are only a few groups, the appearance of the plot can be improved by making the boxes narrower. 
staplewex 
staple line width expansion, proportional to box width. 
outwex 
outlier line width expansion, proportional to box width. 
plot 
if TRUE (the default) then a boxplot is
produced. If not, the summaries which the boxplots are based on
are returned. 
border 
an optional vector of colors for the outlines of the
boxplots. The values in border are recycled if the
length of border is less than the number of plots. 
col 
if col is nonnull it is assumed to contain colors
to be used to colour the bodies of the box plots. 
log 
character indicating if x or y or both coordinates should be plotted in log scale. 
pars 
a list of (potentially many) more graphical parameters,
e.g., boxwex or outpch ; these are passed to
bxp (if plot is true); for details, see there. 
horizontal 
logical indicating if the boxplots should be
horizontal; default FALSE means vertical boxes. 
add 
logical, if true add boxplot to current plot. 
at 
numeric vector giving the locations where the boxplots should
be drawn, particularly when add = TRUE ;
defaults to 1:n where n is the number of boxes. 
The generic function boxplot
currently has a default method
(boxplot.default
) and a formula interface (boxplot.formula
).
If multiple groups are supplied either as multiple arguments or via a
formula, parallel boxplots will be plotted, in the order of the
arguments or the order of the levels of the factor (see
factor
).
Missing values are ignored when forming boxplots.
List with the following components:
stats 
a matrix, each column contains the extreme of the lower whisker, the lower hinge, the median, the upper hinge and the extreme of the upper whisker for one group/plot. 
n 
a vector with the number of observations in each group. 
conf 
a matrix where each column contains the lower and upper extremes of the notch. 
out 
the values of any data points which lie beyond the extremes of the whiskers. 
group 
a vector of the same length as out whose elements
indicate which group the outlier belongs to 
names 
a vector of names for the groups 
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Chambers, J. M., Cleveland, W. S., Kleiner, B. and Tukey, P. A. (1983) Graphical Methods for Data Analysis. Wadsworth & Brooks/Cole.
See also boxplot.stats
.
boxplot.stats
which does the computation,
bxp
for the plotting and more examples;
and stripchart
for an alternative (with small data
sets).
## boxplot on a formula: boxplot(count ~ spray, data = InsectSprays, col = "lightgray") # *add* notches (somewhat funny here): boxplot(count ~ spray, data = InsectSprays, notch = TRUE, add = TRUE, col = "blue") boxplot(decrease ~ treatment, data = OrchardSprays, log = "y", col = "bisque") rb < boxplot(decrease ~ treatment, data = OrchardSprays, col="bisque") title("Comparing boxplot()s and nonrobust mean +/ SD") mn.t < tapply(OrchardSprays$decrease, OrchardSprays$treatment, mean) sd.t < tapply(OrchardSprays$decrease, OrchardSprays$treatment, sd) xi < 0.3 + seq(rb$n) points(xi, mn.t, col = "orange", pch = 18) arrows(xi, mn.t  sd.t, xi, mn.t + sd.t, code = 3, col = "pink", angle = 75, length = .1) ## boxplot on a matrix: mat < cbind(Uni05 = (1:100)/21, Norm = rnorm(100), T5 = rt(100, df = 5), Gam2 = rgamma(100, shape = 2)) boxplot(data.frame(mat), main = "boxplot(data.frame(mat), main = ...)") par(las=1)# all axis labels horizontal boxplot(data.frame(mat), main = "boxplot(*, horizontal = TRUE)", horizontal = TRUE) ## Using 'at = ' and adding boxplots  example idea by Roger Bivand : boxplot(len ~ dose, data = ToothGrowth, boxwex = 0.25, at = 1:3  0.2, subset = supp == "VC", col = "yellow", main = "Guinea Pigs' Tooth Growth", xlab = "Vitamin C dose mg", ylab = "tooth length", ylim = c(0,35)) boxplot(len ~ dose, data = ToothGrowth, add = TRUE, boxwex = 0.25, at = 1:3 + 0.2, subset = supp == "OJ", col = "orange") legend(2, 9, c("Ascorbic acid", "Orange juice"), fill = c("yellow", "orange")) ## more examples in help(bxp)